what model nokia is it and what carrier SIM are you putting into it?
if it was an old tmobile nokia, and youre using an at&t sim, chance are it might not work. most older tmobile GSM phones for use in the US were dual band (900/1900) whereas the older nokias were tri band (850/900/1800). if this is true, your t-mo nokia may not be able to pick up your at&t 850.
if you have tmobile, which uses 1900, then the old nokia which may be at&t branded, may not have the 1900 needed to access the tmobile network.
EDIT: after looking into it, its a Nokia 1200. there are two versions. the US version with 850/1900, which would work with an at&t or tmobile SIM or a european one with 900/1800. so it sounds like youre using a euro model, which is incompatible with US cellular frequencies. this makes it a paperweight in the US and wont work here.