because there inst a t-mobile 3G version currently available. if a t-mobile version is released, then there will be no point in locking them. as of right now though, t-mobile customers still want to use at&t iphones.
What are you talking about?
Tmobile has 3G its just not compatible with iphones. Both AT&T and Tmobile lock their phones no matter what phone it is unless the customer requests an unlock. Then if you get lucky they might give you the unlock code for regural nokias and other phones but that doesnt work with the iphone. AT&T or Apple does not unlock them in the US.