Truphone is a VOIP client that can save you money on your mobile phone calls. Using Truphone over WiFi (WIreless) connectivity your iPhone can make phone calls to landline and mobile numbers. The BBC technology website comments that the Truphone developers plan to implement the ability to also receive phone calls on iPhones. Wi-Fi calls to other connected Truphone users are completely free of charge.
Truphone is available for a few different devices, the iPod Touch, the iPhone, Nokia and Blackberry. Other devices like LG, Sumsung and so on are on the list for future availability. You can register your interest in having the Truphone on your mobile device on their website - http://truphone.com/devices .