UNLOCKED BLACK IPHONE 8GB?

hey im getting an iphone unlocked for tmobile soon so i was wondering what i could do on it. like what can i do that doesnt require the at&t data plan? i know i can get wifi, do any app that requires internet, and apps in general. by the way, are there any apps that i cant do? PS if you add a link to a guide for unlocking/jailbreaking an iphone 3G and 2G then you will have a higher probability of me picking your answer as the best.