My favorite Appon Iphone is Ebuddy, a social app for keeping up with your friends in MSN, Yahoo!, Facebook, Myspace and many more.
I like that it has nice features as emotions, group chat and offline messaging, but what I like most is that you can access all your favorite social sites with a single App!
It's free and can be found at http://itunes.apple.com/gb/app/ebuddy-mess…d320087242?mt=8