Ok, sorry if i posted this in the wrong thread, this is my first time using this site but i plan to stay here

Ok Friday i decided to Jail break and unlock my iphone i used blackra1n and sn0w to do so...

but after i put my cousins tmobile sim in and tried to change the cellular data options i noticed after going to, settings>General>Network> i don't have the cellular data option so what should i do to get this ? i going to be switching to tmobile here shortly but it would suck not to take advantage of mms and data, rite now im using the $3 a day unlimited talk with no data from at&t gophone
My Firm Ware is 3.1.2

any ideas i would truly appreciate, thanks.