Just noticed that as well...never had edge on tmobile and now I do...I know that orange has edge...
I posted a thread a few days ago about only getting GPRS on T-Mobile. Thought it was down to the Sim-card possibly being old, but I guess it could be a network problem?
Maybe they are doing work on the Orange and T-Mobile 3G merger.
trying to force T-Mobile in Androids network settings just gives me the message that my sim card is unable to connect or rejects the connection or some such.
Don't do this, let your phone decide in all cases. You manually setting the network override will achieve close to zero and in most cases will be the wrong thing to do.