Truphone has launched VoIP software for mobile phones to compete with Skype phones.

It is free piece of software that enables Wi-Fi equipped Nokia mobile phones to make internet-rate phone calls (VoIP calls) via Wi-Fi internet connections.  When the phone is not in Wi-Fi range it reverts to being a normal mobile phone.

Skype is available in various guises for mobile phones that pack Wi-Fi but Truphone's trump card appears to be that if someone calls your Truphone number and you’re not ‘on-net’, it simply forwards automatically to your normal GSM number.

Truphone claims it will never cost the caller more, but it may cost them, and you, less (especially if abroad).

The software is SIP based which is a flexible standard to allow different SIP products to talk to each other. The software is still under development and is marked as a beta version.