A recent Digital Nomads post discussed free international calls using a mobile device in combination with VoIP service provider JAJAH. JAJAH Mobile calls can be made without the need for a computer, and enabled by using a mobile plugin that you can download at Jajah Mobile Web. Here is a demonstration video.
Product Description from Demo Dot Com
"The JAJAH Mobile solution allows you to make free international calls directly from your mobile phone. It requires no change of hardware, no new number and no binding contracts. You simply dial the international number, and the JAJAH system takes care of the rest." www.demo.com
Popular mobile devices that work with JAJAH Mobile Web include:
Blackberry, Treo, iPAQ, Smart phones by Motorola, Nokia, SonyEricsson, Samsung. Just to name a few.
JAJAH Mobile Web works with these operating systems:
Windows CE, PocketPC, Symbian OS, MS Smartphone, others.
Web-enabled phone/PDA and service plan. Network charges may apply.
Resources for Portable Professionals and Extreme Telecommuting™