At Cingular, the 120t is a TDMA phone. If you don't already have a TDMA plan, you can't get one, rendering the mobile useless. If you had a TDMA contract from long ago, you can use the 120t, as long as you don't switch your plan. My father is a "grandfathered" customer and Cingular (used to be CellularOne), and has been since nearly the beginning, when they had those damned box/briefcase-sized phones. It's still in our basement. They let him keep his TDMA plan, but come mid-2005, it will be mandatory to switch to a GSM plan.
As for the lock code thing, I believe you can have the phone taken to Cingular to have them wipe it out, or restore the original factory settings. If that fails, and you really want a 120t, I've got an old one around here somewhere, and I'll send it to you if I can find it.
Email me at firstname.lastname@example.org if you'd like the phone, and I'll see what I can do