I'm not sure what "T-Mobile forwarding" means. If you go into the wireless and networks menu, mobile networks and then search for available networks what happens?
It sounds like it might not be like your SIM card, but that is only a guess. Trouble is, if that is the problem it will be trial and error to fix, as the network probably won't help much when they hear it's a no-name Chinese clone - chances are they'll just blame the handset.