
You now will have the ability to make and receive Skype calls and instant message Skype users from your iPhone or iPod touch. Truphone customers on both Apple devices can contact their Skype friends via their Skype IDs.
Truphone-to-Skype communications are free over the Internet, and iPhone users can also place and receive Skype calls and messages when not in a Wi-Fi-accessible location for the cost of a local call, using the Truphone Anywhere feature.

From what I understand, you have to import you Skype/Google Talk/MSN Messenger/Yahoo! Messenger contacts to Truphone in order to communicate with them from the Truphone interface. I'd like an automatic synching capability, but I'll know more when I test it. Of course, the Truphone client on both the iPhone and iPod touch shows who is online with its presence capabilities.
Truphone is one of the "must" have apps for the iPhone & iPod touch. I should mention that I also like fring because it has a native SIP client built in that lets you specify your own SIP credentials. That's one thing lacking in truphone. truphone is based on SIP, but it goes through their SIP-to-PSTN network. AFAIK you can't change it to your own SIP credentials. I guess that would cut into their revenue/business model. Though fring appears to be surviving - at least for the moment. I believe fring is experimenting with mobile ads though.