It's Tru. They removed the 'phone' from Truphone and renamed it Tru. Truphone, so now Tru, is a mobile VoIP service that offers roaming everywhere in the world at local rates. What's also Tru is that they have released an application for desktop computers and laptops.
Users can use both the mobile app and the computer app interchangeably - such that a call can be transferred from one to the other in the eventuality of having to move, or entering home. Actually, both apps ring and you can choose where to take the call. Tru's new app is available for Windows XP/7, for Mac OS and for all the major versions of Linux.
Tru offers roaming calls at local rates, which is an improvement in itself for travelers, and an improvement over traditional phone, but the rates aren't the lowest among VoIP providers. I'd keep it to what they do best, roaming.