An IP phone is a telephone service that conducts voice calls using Internet Protocol (IP). Instead of traditional analog lines, it transmits voice data as packets over internet connections. Built on VoIP technology, IP phones are assigned numbers beginning with 050. While VoIP is the general term for the technology, IP phone refers to the service that comes with a phone number.
The differences from Hikari Denwa (fiber-optic phone) can be summarized in three points. First, the numbering system: 050 IP phones do not have an area code, so the caller's region cannot be identified, whereas Hikari Denwa can use existing landline numbers (like 03 or 06). Second, emergency calls: 050 numbers cannot dial 110/119, but Hikari Denwa supports them. Third, cost: 050 numbers tend to have lower monthly fees, with some services being free, while Hikari Denwa is 550 yen per month on NTT East's basic plan (tax included, as of August 2026) and requires a fiber-optic subscription through FLET'S Hikari or a collaboration provider.
IP phone call quality depends on the quality of the internet connection. In environments with sufficient bandwidth and low latency, call quality is comparable to landline phones. However, in areas with weak Wi-Fi signals or during congested mobile data periods, voice interruptions and delays can occur. The choice of codec also affects quality - G.711 (high quality, high bandwidth) and G.729 (lower quality, low bandwidth) produce different audio experiences.
An important practical note: a 050 number gives the person receiving the call very little to go on. It carries no area code, so the digits say nothing about where the caller is, and because some services can be signed up for entirely online, 050 numbers turn up as the origin of sales calls and robocalls. At the same time, many companies and individuals use 050 numbers for ordinary business to keep call costs down. Blocking every 050 call on the assumption that it must be trouble is the pitfall: you end up missing calls you needed to take. For a 050 number you do not recognize, the safe course is to check the caller with a phone number lookup service before calling back. You can learn about the technical background in VoIP basics and benefits and find specific defense strategies in IP phone spam countermeasures.