Hikari Denwa is an IP phone service provided by NTT East/West that uses fiber-optic lines (FLET'S Hikari). Built on VoIP technology, its distinguishing feature is that it can be used just like a traditional analog phone. Since its launch in 2004, it has become the mainstream landline service, with over half of NTT's landline subscriptions having migrated to Hikari Denwa.
There are three major differences from 050-number IP phones. First, you can keep your existing landline number (with area code), eliminating the hassle of number changes and updates to business cards or websites. Second, it supports emergency calls (110/119), which 050 IP phones cannot make - a significant differentiator. Third, call quality is comparable to analog phones, as voice is transmitted within NTT's closed IP network, designed to be less affected by internet congestion.
In terms of pricing, the monthly base fee of 550 yen (tax included) and nationwide flat rate of 8.8 yen per 3 minutes are major attractions. Compared to the traditional analog line base fee (1,760 yen for residential use), it's about one-third the cost, with significantly cheaper long-distance rates. However, Hikari Denwa requires a FLET'S Hikari subscription, so total costs including internet fees (approximately 4,000-6,000 yen/month) should be compared. For households already using internet, the additional cost is just the 550 yen base fee.
Note that Hikari Denwa cannot make calls during power outages. Analog lines operated on minimal power supplied from the telephone exchange and worked during outages, but Hikari Denwa requires power for the optical network terminal (ONU) and router. Installing a UPS (uninterruptible power supply) or keeping a mobile phone as backup is important. Review migration procedures in the Hikari Denwa migration guide and technical background in VoIP basics and benefits.