I'm also with T-Mobile and exactly the same thing a few weeks ago after the T-mobile upgrade, went from a 6230 to a 6290. It was painless.

Backed up the 6230

Removed the pin card fro the 6230 and put it in the 6290. It fired right up.

Restored the *data* to the 6290 and resent the service books to the 6290.

The 6290 then asked me if I wanted my existing email account reassigned to the 6290's IEMI ....