iPhone after contract

I've already got AT&T, and my contract's been up for a while.  I've been looking at "smartphones", and somehow the iPhone seems like the best solution.  If I got a new phone after two years, do you know if I could keep using the iPhone for applications/ WiFi?  I guess this is the equivalent of asking if I can do that stuff without a SIM card.  Maybe someone could try it if you don't already know?

Thanks

Shit, sorry, I should have put this in tech, but I was thinking "after being a phone, it would become just a computer".

You will need a sim card in the phone for it to work. You can just use a unactivated AT&T one or you can just buy the gophone kit and use that.

GSM IS DEAD

Thanks for the suggestion.  Also what the hell does GSM being dead have to do with this?  Hell, it might be relevant, I don't know enough about phones.