Glossary
Definitions of phone number terminology. Learn about area codes, prefixes, and other phone number-related terms.
RCS (Rich Communication Services)
The successor to SMS. A next-generation messaging standard supporting image sharing, group chat, and read receipts.
ISDN
A digital telephone line service. NTT's INS Net is the representative example.
IP Phone
A phone service that uses internet connections. The 050 number series is representative, offering low call rates.
IVR (Interactive Voice Response)
A system that plays automated voice guidance on incoming calls and routes callers to appropriate departments via keypad input.
Interactive Voice Response
An automated phone system that uses voice prompts and keypad input to route callers to the appropriate department or information.
i-mode
NTT Docomo's 1999 mobile internet service for feature phones, a pioneer of pre-smartphone mobile internet.
Analog Line
A traditional phone line that converts voice signals directly into electrical signals for transmission.
Encryption
Technology that converts communication content into an unreadable format for third parties, essential for preventing call and message interception.
E.164
An international phone number format standard defined by the ITU. Notation like +81 3 1234 5678.
eSIM
A rewritable SIM embedded in the device. Enables online activation without a physical card.
Web Real-Time Communication
An open technology enabling real-time voice and video calls directly in web browsers without app installation.
Satellite Phone
A phone that communicates via satellites. It can make calls outside mobile coverage and is invaluable during disasters.
ACD (Automatic Call Distribution)
A system that automatically routes incoming calls to the best-suited operator based on skills and wait time in a call center.
Asymmetric Digital Subscriber Line
High-speed internet technology using existing copper telephone lines, discontinued in 2024 as fiber optic lines became dominant.
APN (Access Point Name)
Configuration settings your phone needs to connect to the internet. Manual setup may be required when using budget SIM cards.
SMS (Short Message Service)
A service for sending and receiving short text messages to phone numbers.
Near Field Communication
Short-range wireless technology operating within 10cm, powering Osaifu-Keitai and Apple Pay contactless payments.
MNP (Mobile Number Portability)
A system that allows switching carriers without changing your phone number. Introduced in Japan in 2006.
Mobile Number Portability
A system allowing mobile users to switch carriers while keeping their phone number, introduced in Japan in 2006.
MVNO (Budget SIM)
A mobile virtual network operator that provides services by leasing lines from major carriers.
Mobile Virtual Network Operator
A carrier that provides mobile services by leasing network capacity from major carriers, commonly known as budget SIM providers.
Area Mail
NTT Docomo's emergency alert service that broadcasts earthquake warnings and tsunami alerts to all devices in the affected area.
Long Term Evolution
The 4th generation (4G) mobile communication standard enabling high-speed data and high-quality VoLTE voice calls.
Osaifu-Keitai
A Japan-originated mobile payment technology using FeliCa chips, enabling contactless payment and authentication by holding the phone near a reader.
Operator
A person who handles call routing and customer inquiries. The core workforce of call centers.
It's-Me Scam
A phone scam where the caller impersonates a family member and urgently demands money, the most iconic type of special fraud in Japan.
Voice Guidance
Pre-recorded announcement messages played during automated phone responses, used in IVR and voicemail systems.
Voice Clone Scam
A new fraud technique that uses generative AI to mimic a specific person's voice and impersonate family or acquaintances over the phone.
Speech Synthesis
Technology generating artificial speech from text data, used in IVR announcements and exploited in voice clone scams.
Voice Call
Real-time voice conversation over telephone or internet lines, the fundamental purpose of phone systems.
Voice Recognition
Technology enabling computers to interpret human speech as text or commands, powering Siri and Google Assistant.
Circuit Switching
A communication method that dedicates a circuit between caller and receiver for the call's duration, the foundation of traditional telephone networks.
Fictitious Billing
A fraud scheme demanding payment for services never used, delivered via SMS, postcards, or phone calls.
Virtual Phone Number
A phone number managed in the cloud without being tied to a physical line.
Subscriber Number
The trailing portion of a phone number that identifies individual subscribers.
Feature Phone
A colloquial term for pre-smartphone flip phones that evolved uniquely in Japan, nicknamed 'Galapagos phones.'
Garaho
A mobile phone combining a feature phone's physical button design with Android OS, offering smartphone capabilities in a traditional form factor.
Base Station
Wireless equipment that connects mobile phones to the carrier network. The key to area coverage.
Airplane Mode
A feature that disables all wireless transmissions on your phone. Useful not just on planes but also when you need to focus.
Basic Charge
A fixed monthly fee for maintaining a phone line, charged regardless of whether calls are made.
Reverse Lookup
A search method that identifies the owner or business from a phone number - the reverse of a standard phone directory.
Call Waiting
A service allowing users to put a current call on hold and answer a new incoming call during conversation.
QoS (Quality of Service)
Technology that guarantees communication quality. A mechanism that prioritizes voice call packets.
Earthquake Early Warning
A system that issues warnings before earthquake shaking arrives, forcibly notifying all smartphones in the affected area.
Emergency Call System
Japan's emergency call system connecting callers to police (110), fire/ambulance (119), and coast guard (118) free of charge.
Emergency Number
Special numbers for emergencies including police (110), fire/ambulance (119), and coast guard (118).
Cooling-Off
A consumer protection system allowing unconditional contract cancellation within 8 days for telephone solicitation sales.
Cooling-Off
A consumer protection system allowing unconditional contract cancellation within a set period for door-to-door and telemarketing sales.
Country Code
A number that identifies a country for international calls. Japan is +81, the United States is +1.
Cloud PBX
A virtual telephone exchange operating in the cloud. Enables extension calls from any location.
Cloud PBX
A service providing PBX functionality in the cloud, enabling smartphones as extensions without physical equipment.
Black Rotary Phone
An iconic Showa-era landline telephone characterized by its black casing and rotary dial.
Mobile Phone Number
An 11-digit phone number starting with 090, 080, or 070. Approximately 190 million lines are in use.
Out of Range
A state where mobile phone signals cannot reach, preventing calls and data communication, common in mountains, underground, and inside buildings.
Telephone Exchange
Telecommunications equipment that connects callers to recipients, evolving from manual switchboards to automatic and IP-based systems.
Public Phone
Shared telephone units installed in public spaces, operated with coins or prepaid telephone cards.
Codec
Technology that compresses and decompresses audio data. Determines the balance between call quality and bandwidth.
Cordless Phone
A landline phone with wirelessly connected base and handset units, allowing free movement within the home during calls.
Call Center
A department or facility specializing in phone-based customer service. Comes in inbound and outbound types.
Callback
Returning a phone call; also a call center service offering to call customers back instead of keeping them on hold.
International Call
A phone call made between different countries. Connected using the country code and access code 010.
Personal Information
Information that can identify a specific individual, such as name, phone number, and address, regulated by Japan's Personal Information Protection Act.
Landline Phone
A telephone connected to a line installed at a fixed location. The area code identifies the geographic region.
Vanity Number
A memorable phone number where digit readings form words. Used in corporate advertising strategies.
Disaster Message Dial
An NTT service that allows recording and playing back safety confirmation messages via 171 during major disasters.
Silent Mode
A smartphone setting that disables all ringtones, notification sounds, and vibration for complete silence.
Three-Way Calling
A phone service enabling three people to talk simultaneously, used for business conference calls and family consultations.
CTI (Computer Telephony Integration)
Technology that links computers with phone systems to automatically display customer information on incoming calls.
Global Positioning System
A satellite-based system for determining device location, used for emergency call positioning and smartphone tracking.
Area Code
A regional identification number at the beginning of a landline phone number. 03 indicates Tokyo's 23 wards, and 06 indicates Osaka City.
Area Code
The leading digits of a phone number indicating geographic area, such as 03 for Tokyo's 23 wards and 06 for Osaka.
Area Code Map
A visual map showing the correspondence between area codes and geographic regions.
SIP (Session Initiation Protocol)
A communication protocol that controls call setup and teardown for IP phones. The standard for VoIP.
Auto Attendant
A system that automatically answers incoming calls and guides callers with voice prompts.
Time Signal
A service providing accurate time announcements by calling 117, offered by NTT for 11 yen per call.
SIM Card
A small IC card that stores mobile phone subscriber information. Linked to a phone number.
SIM Swap
An attack technique that fraudulently transfers someone's phone number to the attacker's SIM.
SIM-Free
A device state allowing use with any carrier's SIM card, not locked to a specific operator.
Consumer Hotline
A consultation service reached by dialing 188, connecting callers to local consumer affairs centers for commercial fraud and contract disputes.
Shoulder Phone
Japan's first mobile phone from 1985, weighing about 3kg and carried on the shoulder with a strap.
STIR/SHAKEN
A protocol that verifies caller ID authenticity using cryptographic signatures. The international standard for combating number spoofing.
Spam
Unsolicited bulk communications including calls, SMS, and emails, often sent via automated dialing systems.
Smishing
Phishing fraud via SMS. Directs victims to fake websites to steal personal information.
Smishing
Phishing attacks conducted via SMS messages containing fraudulent URLs to steal personal information or money.
3rd Generation Mobile
The 3rd generation mobile standard that supported i-mode and feature phone culture, now being shut down by carriers.
Infrared Communication
Short-range data transfer technology using infrared light, widely used for contact exchange during the feature phone era.
0120 Number
A toll-free number where the receiver pays call charges, widely used for corporate customer service lines.
050 Number
Numbers assigned to IP phones, not tied to geographic areas, obtainable at low cost but unable to make emergency calls.
0570 Number
A Navi Dial number with nationwide flat-rate charges for callers, used by corporate call centers but excluded from unlimited calling plans.
Social Engineering
An attack method that exploits human psychological vulnerabilities rather than technical means to extract confidential information.
Dark Web
A hidden part of the internet accessible only through specialized software, often exploited for trading stolen personal information.
Bandwidth
The maximum data capacity a communication line can transfer at once; wider bandwidth enables faster, higher-capacity communication.
Bandwidth
The amount of data a communication line can transmit at once. A metric directly tied to call quality.
Main Number
An organization's primary contact phone number, distributed to multiple extensions via PBX.
Dial-In
A service that allows multiple phone numbers on a single line. Used for corporate extensions.
Dial-In
A service assigning multiple phone numbers to a single line, routing each number directly to a specific extension.
Dial Q2
A premium-rate telephone information service that caused billing scandals and was discontinued in 2014.
Speed Dial
A feature that registers frequently used numbers under short codes for quick dialing.
Ringtone
The sound that alerts you to an incoming call. Customizable by contact or purpose.
Toll-Free Number
A general term for phone numbers where the receiving party pays call charges. 0120 and 0800 numbers fall into this category.
Call Blocking
A feature that automatically blocks incoming calls from specific phone numbers or anonymous callers.
Call Rejection
A feature that automatically blocks incoming calls from specific numbers or withheld numbers. A fundamental defense against nuisance calls.
Call Transfer
A service that automatically forwards incoming calls to another number, useful when away or unavailable.
Ringtone Melody
Melodies played for incoming calls; ringtone and ringback tone downloads were a major business during the feature phone era.
Call History
A log of incoming and outgoing calls. Important not just for checking missed calls but also for preserving evidence against harassment.
Trunk Line
High-capacity communication lines connecting telephone exchanges.
Telecommunications Carrier
A major telecommunications provider that owns its own network infrastructure. Four carriers operate in Japan.
Network Outage
An event where phone and data services become unavailable due to equipment failure or overload, with large-scale outages becoming social issues.
Communication Speed
A measure of data transmission rate in bps (bits per second), directly affecting call quality and app performance.
Secrecy of Communications
A right guaranteed by Japan's Constitution and Telecommunications Business Act protecting communication content and records from third-party access.
Call Charges
Fees incurred when making phone calls. Pricing structures differ between landlines, mobile phones, and IP phones.
Call Recording
A feature that records phone conversations as audio data. Used for evidence preservation and quality management.
DTMF (Dual-Tone Multi-Frequency)
Audio signals generated when pressing phone buttons. Used to operate automated response systems.
Data Communication
Communication of digital data other than voice (text, images, video) over networks.
Data Usage
The amount of data consumed when using the internet on your smartphone, colloquially called 'giga' in Japan.
Tethering
A feature that shares your smartphone's mobile data connection with other devices, turning it into a Wi-Fi hotspot.
Dual SIM
A feature that allows two SIMs (phone numbers) to be used simultaneously on a single smartphone.
Dual SIM
A feature allowing two SIM cards in one smartphone, enabling simultaneous use of two phone numbers.
Telephone Card
A prepaid card for public phones, gaining renewed attention as a disaster communication tool.
Telephone Card
A prepaid card for public phones, available in 50-unit (500 yen) and 105-unit (1,050 yen) denominations.
Telemarketing
A marketing method that uses phone calls to promote products and services.
Telework
A work style using ICT to work outside the office, supported by phone systems, video calls, and cloud PBX.
Telecommunications Business Act
A law defining carrier obligations and user rights, serving as the legal basis for communication privacy and anti-nuisance measures.
Disaster Message Dial
A voice message service accessible by dialing 171 during disasters, provided by NTT for safety confirmation.
Call Forwarding
A service that automatically forwards incoming calls to another phone number. NTT's Voice Warp is representative.
Radio Wave
Electromagnetic waves used for mobile phones and wireless communication, with range and building penetration varying by frequency band.
Conference Call
A service that allows three or more people to talk simultaneously. Usage has grown with the spread of remote work.
Telephone Line
A communication circuit for transmitting voice calls, including analog, ISDN, fiber optic, and mobile network types.
Telephone Subscription Right
A one-time fee for the right to use an NTT landline. Once valued at 72,000 yen as an asset.
Telemarketing
A sales method using phone calls to promote products or services, regulated under Japan's Specified Commercial Transactions Act.
Do Not Call
A system for registering your intent to not receive sales or solicitation calls.
Phone Anxiety
A condition of intense anxiety or fear about making or receiving phone calls.
Telephone Exchange
Telecommunications equipment that connects and switches phone lines. The core of the telephone network.
Telephone Operator
A profession operating manual switchboards to connect callers, made obsolete by automatic exchange technology.
Phone Scam
A general term for crimes that use phone calls to steal money or personal information. Annual losses reach tens of billions of yen.
Phone Directory
A listing that maps phone numbers to names. Has evolved from paper directories to smartphone contacts.
Phone Book
A directory mapping phone numbers to names. From paper directories to smartphone contacts apps, the format keeps evolving.
Phone Harassment
Harassment conducted via telephone. Includes repeated calls and threatening conversations.
Phone Number Lookup
A service for looking up caller information from a phone number. An essential tool for identifying nuisance calls.
Phone Number Validation
The process of verifying whether an entered phone number is in a valid format.
Phone Number Format
Rules for writing phone numbers. Covers hyphen placement and international notation.
Caller ID Display
A general term for the feature that displays the caller's phone number on screen during incoming calls. The foundation of nuisance call defense.
Phone Number Privacy
The protection and management of personal information associated with phone numbers.
Phone Number Recycling
A system where canceled phone numbers are reassigned to new users after a cooling-off period.
Phone Etiquette
Proper manners for making and receiving phone calls. Especially important in business settings.
Telephone Relay Service
A service where operators mediate phone calls between deaf/hard-of-hearing and hearing individuals, established as public infrastructure in 2021.
Phone Tree
A contact system where people call each other in sequence to relay information during emergencies.
Phone Tapping
The act of a third party illegally intercepting call content. Strictly regulated under the Telecommunications Business Act.
DTMF Tone Signal
Dual-frequency tones generated by pressing phone buttons, used for IVR navigation and telephone service authentication.
Special Fraud
An umbrella term for fraud committed remotely via phone or electronic communication, classified into 10 types by Japan's National Police Agency.
Special Number
Short phone numbers assigned to specific services. Examples include 104 (directory assistance) and 117 (time announcement).
Specified Commercial Transactions Act
A law that regulates 7 transaction types including telephone solicitation sales to protect consumers.
Extension Line
An internal phone line within an organization connected through a PBX, enabling free intra-office calls without external lines.
Extension Number
A number assigned to identify individuals or departments within an organization.
Navi Dial
A nationwide unified number starting with 0570. Call charges are paid by the caller and excluded from unlimited calling plans.
Spoofing
The act of impersonating another person or organization via phone, email, or SMS to deceive victims into surrendering information or money.
Number Display
An NTT service that displays the caller's phone number on landline phones during incoming calls.
Number Request
An NTT service that prompts withheld-number callers to redial with caller ID enabled. Widely used on landlines against nuisance calls.
Two-Factor Authentication (2FA)
A security method that verifies identity using a second factor such as an SMS code in addition to a password.
Packet Communication
A communication method dividing data into small packets for transmission, sharing lines for high efficiency.
Caller ID Spoofing
A technique that displays a different phone number than the actual caller on the recipient's device. Sometimes abused for fraud.
Caller ID
A feature that displays your phone number on the recipient's device when making a call.
Hello Page
NTT's personal name telephone directory, discontinued in 2023 due to privacy concerns.
Directory Assistance
A service for looking up phone numbers by name and address by calling 104, available for 66 yen per inquiry.
Caller ID Spoofing App
An app that changes the displayed caller ID to any number. Misuse for fraud is a serious problem.
Numbering Plan
A plan defining telephone number structure and allocation rules, managed by Japan's Ministry of Internal Affairs including number exhaustion countermeasures.
Number Exhaustion
The problem of running out of available phone numbers. Japan has responded by expanding from 090 to 080 and then 070.
Number Block
A group of phone numbers classified by their leading digits. Assigned by purpose or region.
Number Portability
A general term for systems that allow changing carriers or services without changing your phone number.
Number Allocation
A system in which the Ministry of Internal Affairs and Communications assigns phone number blocks to carriers under the Telecommunications Numbering Plan.
Act on Prevention of Transfer of Criminal Proceeds
A law preventing money laundering and terrorist financing, regulating fraudulent mobile phone contracts and bank account trading.
Handover
Technology that automatically switches the connected base station during movement. Prevents call drops.
PHS (Personal Handy-phone System)
A lightweight mobile phone system originating in Japan. It used 070 numbers and all services ended in 2023.
PSTN (Public Switched Telephone Network)
The traditional analog landline telephone network. Migration to IP networks has been underway since 2024.
Public Switched Telephone Network
The traditional circuit-switched public telephone network, transitioning to IP networks from 2024.
PBX (Private Branch Exchange)
A telephone exchange system that manages and controls phone lines within an organization.
Private Branch Exchange
A private telephone switching system within an organization that manages internal extensions and external line connections.
Fiber Optic Line
A high-speed communication line using optical fiber, used for Hikari Denwa phone service and internet connectivity.
Hikari Denwa (Fiber-Optic Phone)
An IP phone service using fiber-optic lines. Provided by NTT East/West.
Business Phone
A multi-function phone system for offices. Supports extension calls, transfers, hold, and shared lines.
Visual Voicemail
A feature that displays voicemail messages in a list for selective playback.
Withheld Number
A calling feature that hides the caller's phone number from the recipient by dialing 184 before the number.
Anonymous Call
A call made without notifying the caller's number. Made by dialing 184 before the number.
Vishing
Phone-based phishing fraud. A technique that extracts personal information through voice calls.
Video Call
A call format transmitting both audio and video in real time, used through Zoom, FaceTime, LINE, and similar platforms.
PIN Code
A short numeric password used to unlock SIM cards and smartphones.
5G (Fifth Generation Mobile Network)
The fifth-generation mobile communication system. Delivers ultra-high speed, ultra-low latency, and massive simultaneous connections.
FAX (Facsimile)
A communication method for sending and receiving documents and images over phone lines. Japan is one of the world's heaviest users.
Fax
A technology for transmitting documents and images over telephone lines, still widely used in Japanese government, healthcare, and real estate sectors.
VoIP
A general term for technology that enables voice calls over internet connections.
Phishing
A fraud technique that steals personal information using fake websites and messages.
Virtual Private Network
Technology that creates an encrypted virtual private tunnel over the internet to enhance communication security.
Filtering
A system that automatically blocks harmful websites and nuisance calls. Legally required for minors' smartphone use in Japan.
Push Notification
Automatic alerts sent from apps and services to your smartphone, used for message notifications and news updates.
Push-Button Phone
A button-operated telephone replacing rotary dials, using DTMF signals essential for IVR and automated service navigation.
Free Dial (Toll-Free Number)
A 0120 number service where the receiving party pays the call charges. A registered trademark of NTT Communications.
Bank Transfer Fraud (Furikome Sagi)
A collective term for special fraud that tricks victims into transferring money through phone deception.
Bank Transfer Fraud Relief Act
A 2008 law enabling freezing of fraud-linked bank accounts and returning stolen funds to victims.
Prepaid Phone
A mobile phone that works only with pre-charged credit. No monthly fees, but associated with criminal misuse concerns.
Prepaid SIM
A SIM card with pre-paid usage for a set period or data amount, suited for travelers and short-term use.
Bluetooth
A short-range wireless communication standard used to connect devices like earphones and speakers.
Prefix
A general term for the leading digits of a phone number. Includes area codes, mobile identification numbers, and service numbers.
Broadband
A general term for high-speed, high-capacity internet connections including ADSL, fiber optic, and cable TV lines.
Protocol
Standardized rules for data exchange between communication devices, with SIP, RTP, and TCP/IP used in telephony.
Voicemail
A service that records and stores callers' voice messages when unavailable, the digital evolution of answering machines.
Pager
A portable wireless device for receiving numeric or kana text messages, hugely popular among Japanese youth in the 1990s.
Hotline
A dedicated phone line for emergencies or specific consultations. Used by government helplines and corporate emergency contacts.
Hold Music
Music or melodies played during a phone call hold, influencing brand image and customer experience.
VoLTE (Voice over LTE)
Technology that delivers high-quality voice calls over 4G LTE. Offers better audio and faster connection than 3G calls.
Manner Mode
A phone setting that silences ringtones and alerts, notifying only by vibration - a term unique to Japan.
Silent Call
A call where the other party says nothing after you answer. Main causes include harassment and auto-dialer malfunctions.
Data Broker
Businesses that collect and trade personal data, serving as a pipeline for leaked phone number lists reaching fraud groups.
Nuisance Call
A general term for unwanted phone calls. Includes sales calls, solicitations, scam calls, and silent calls.
Spam Call Filter
A feature that automatically identifies potentially nuisance incoming calls and provides warnings or rejection.
Modem
A device converting between digital data and analog signals, used for dial-up internet and fax communication.
Premium Rate Number
A phone number with higher-than-normal call charges. The 0570 Navi-Dial is the most common example in Japan.
Universal Service
Basic telephone services guaranteed to be available equitably nationwide, covering subscriber lines, public phones, and emergency calls.
Redial
A one-touch function to re-call the last dialed number, used for redialing busy or unanswered calls.
Voicemail
A service that records caller messages when you are unavailable.
Latency
Delay time in communications. For phone calls, under 150 ms is the benchmark for comfortable conversation.
Roaming
A system that allows calls and data on another carrier's network when outside your own carrier's coverage area.
Robocall
Phone calls mass-dialed by automated systems playing pre-recorded messages.
Wi-Fi
Wireless communication technology based on IEEE 802.11 standards, widely used for smartphone calls and data transmission.
Wi-Fi Calling
A feature that enables mobile voice calls over a Wi-Fi network. Useful indoors where cellular signal is weak.
Wangiri (One-Ring Call)
A technique of ringing once and hanging up to lure a callback. Common in international phone fraud.
One-Ring Scam (Wangiri Fraud)
A scam technique that rings once and hangs up, luring victims into calling back premium-rate numbers.
One Seg
A mobile digital terrestrial TV broadcasting service viewable on feature phones and car navigation systems.
One-Time Password
A single-use disposable password delivered via SMS or authenticator apps, widely used for two-factor authentication.