Probably not. At least not in the same form. If it did go to T-mobile it would be changed in design aspects or even somewhat in performance aspects from the AT&T version. I have yet to see the same exact phone release on the big four carriers. Even with the GSII, there were differences in screen size and even the T-Mobile version didn't have the same processor. Also, I haven't seen the FCC filing but lately both AT&T and T-Mobile have been releasing phones with extra radio waves to make sure they are compatible with the other because of the merger that has yet to happen. That is most likely your best bet for getting the Titan. OR, you can buy it unlocked a few months from now for a lot of money.
On the bright side, T-Mobile has a long history with Nokia so you can probably get whatever device they release.