this doesn't answer the OP's question, but, i have a sim unlocked att G2 and i can get 4G and 4G LTE service with my T-Mobile sim/account. coverage is not as good as at&t in my location.
d.cortez || HTC One (M8) || SGN 3 || Nexus 7 (LTE)
"My life has no purpose, no direction, no aim, no meaning, and yet I'm Happy. I can't figure it out. What am I doing right?" --Snoopy