I’ve just installed Truphone on my Nokia E65. What a brilliant VoIP application – free calls using my home WiFi router from my mobile phone. It seamlessly integrates with the E65 software so when making a call, the handset will automatically attempt to complete the call via WiFi and if there’s no WiFi available it will use the cellular network.
Truphone gives you another mobile number which will deliver calls to your handset via WiFi when in coverage or via forwarding to your regular mobile number when Truphone isn’t available (outside WiFi coverage). Calls to other Truphone users are free and until the end of June calls to 40 countries worldwide are also free.
The Truphone blog is worth a read.