The iPhone 3GS was an excellent phone -- 18 months ago. But there's a lot you can do now with iOS that seems clunky on the 3GS, i.e. Facetime and Skype video chatting with ease. iPhone 4 is also a faster experience, and the retina screen causes far less eye strain. If you sign up for a two year contract with 3GS, that's a long time to go with yesterday's tech.