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.
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.