I have an ATT Palm Centro that I just unlocked for T-Mobile (for some reason the code has to be inputted multiple times for it to actually accept it *#*#code# but thats besides the point)

The question is, when i place the ATT sim card in, the phone picks up the ATT network just fine. However, when i place the T-Mobile sim card in, it does nothing.... i tried looking at the settings to see if i could change the bands or something but couldn't find anything....any suggestions?