1.i have a tmobile sidekick and i want the iphone but what will happen to my contract. will my internet still work?
2. jailbroken means adding a 3rd party... but what does that really mean?
3. when i get updates how do i unlock my phone again and will i have to jailbreak it again too?

basically any more information i can have on buying an unlocked iphone and having it for tmobile. and problems i should be running into?