I believe fring was the first to bring Skype calling capability to the iPhone back in October 2008. Today, Truphone announced the upgraded version of Truphone that will support Skype calling and instant messaging functions. With Truphone you can also place Skype calls without a WiFi connection and be billed just for your cellular plan minutes thanks to Truphone Anywhere.
The upgraded client will be available sometime next week, week of 12 January, but you can see it in action at Macworld 2009 at the Truphone stand. It looks like the iPhone and iPod touch have revived interest in Truphone and the more people that download and use it the more free calls people can make since Truphone-to-Truphone calls are always free.
The second part of Truphone's announcement was in regards to instant messaging with other IM clients. iPod touch users have had some IM support on the Truphone client and now iPhone users will get this functionality with all users getting improved capability. You can now use Truphone for two-way IM over Windows Live Messenger, Yahoo! Messenger, and Google Talk. You can also make and received voice calls over Google Talk, with support for Windows Live and Yahoo! coming soon. Twitter is now also integrated with TruFriends view.
It looks like Truphone is definitely making a push to be THE communications client on the iPhone and iPod touch. The Truphone client also supports presence functionality so you know who is online with what service.