Carriers like to throw around the term "unlimited mobile-to-mobile" from time to time, but we don't think this is exactly what they had in mind. ROK's "Viper" VoIP client uses a handset's Bluetooth link to hook it up to a PC sporting a broadband Internet connection, which in turn connects it to any other handset with Viper installed. Better yet, Viper contacts are shown with their availability in a buddy list format -- but the best part? It's all completely free and covers platforms Skype doesn't. Compatibility is limited to a handful of Nokia handsets running S60 right now, but word on the street has ROK releasing on Java and Windows Mobile clients before too long.
[Via Tech Digest]