Well, the D2G won't even work on T-Mobile without both SIM and band unlock. And even after that she will only ever get 2G, as only phones made for T-Mobile support their retarded 1700MHz band.
To perform SIM unlock first try eBay stuff like unlock_fusion and the likes, they refund if the code doesn't work and you present a video proof of it.
For band unlock, refer to a thread about it in this forum section.
to be fair, TMO is supposed to be moving HSPA out of the 1700 band and into the 1900/2100. LTE is supposed to be going in the 1700 band. Whenever that happens...the d2g will be good to go.
Not disagreeing with you about your comment though lol. They are the only provider in the world I think that uses the 1700 band for HSPA.