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 costs 550 yen per month but requires a fiber-optic internet subscription.
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: 050 numbers are frequently abused for nuisance calls. Because acquisition costs are low (free to a few hundred yen per month) and some services have lax identity verification, they are used as sources for sales calls and robocalls. For suspicious calls from 050 numbers, it is safest to check the caller using a phone number lookup service before responding. You can learn about the technical background in VoIP basics and benefits and find specific defense strategies in IP phone spam countermeasures.