Im guessing that you know by know that Apple reported 100 new features in the new iPhone OS 3.0 . No matter if some of them seem identical, there are 100 new features and pretty much this OS rocks.If you dont know all of them , you can check them out in the link above. You can find , though, a lot of hidden features inside this new OS.
Hidden Features of iPhone OS 3.0
Tons of hidden features in iPhone OS 3.0