People have the Titan 2 running on Tmobile's 3g network, so I think its possible for the 900 to run on Tmo as well.
Not saying it isn't possible, just that it's been tried and hasn't worked. The radio on these devices is capable of working but is also capable of being locked out (ie. AT&T skyrocket users had to flash a radio to get it to work on Tmo).