T-Mobile USA has gone ahead with its fixed line VoIP service with the commercial launch last week. While its parent company T-Mobile is testing Femtocell based convergence elsewhere in several countries, the US based arm decided to leverage the ubiquitous WiFi instead.
Femtocell has been in vogue throughout 2007. Faced with the prospect of possible GSM-to-WiFi traffic substitution due to FMC, nearly all major cellular operators have been exploring the Femtocell based FMC that helps you stalk your customer all the way around his house. However, Femtocells are not widely deployed yet and they deal with licensed spectrum making management rather complex. WiFi on the other hand is unlicensed and ubiquitous.
T-Mobile USA started with a WiFi-GSM dual mode FMC offering in June 2007. Those who bought the dual mode handsets transparently handed over the traffic to WiFi at home which eased some load off T-Mobile GSM switches and came out of the usual bucket of minutes. For an additional $20/month you could then ask for unlimited Voice-over-WiFi calls, separate from the usual bucket of GSM minutes.
The fixed line VoIP offering is different in the sense that it comes with a different phone number. The customer pays $10/month extra for unlimited calls. Not sure if there are features like simultaneous ring, but that sort of functionality is a standard feature now.
It must be a challenge to convey the confusing tariff plans here and the difference between the plans. The other issue is that with the landline service the customer has to buy a new WiFi router that comes with an ATA.