Garrett Smith, one of the guys behind the success of VoIP Supply, has launched a side project called Mobile VoIP Review where users can rate, write reviews, and discuss voice over IP providers that can be used on your mobile handset. Some of the providers represented on this site include: Truphone, Mobivox, Rebtel, Fring, Jajah, and several others I hadn't heard of.

The term "Mobile VoIP" means calling a local access number to make a cheap International call (e.g. Jajah, Mobivox, Rebtel) or making a call over a data connection (e.g. Fring, Truphone). Of course, there are plenty of other companies that could be added to this list as well, but it's a starting point for those looking for information.