Buddy wants me to unlock Iphone4 to use on T-Mobile

[MustangLife]

I have 2 and half years experience jailbreaking but never an unlock. I don't see it being hard. But is there an issue doing a Iphone4 on T-Mobile. It is a at&t iphone4. I told him he should just do a Iphone4S on sprint,verizon or at&t. He won't be able to get 3G service with a t-mobile unlocked iphone4 made for at&t correct? Hes in the middle of a t-mobile contract. Its possible to get out of it right.

Josh

 

[jeffrey1027]

To get out of contract, you have to pay an early termination fee of up to $300 depending how much months is left
i4 will only get 2g on t mobile
If the iPhone has a baseband of 1.59.0 or something with a 1, you can install ultrasn0w from Cydia an unlock
Another option is using a gevey sim unlock. Thy are cheap online $10-$30 max