Motorola E680i unlocked only works on some towers?

i have cingular service using a triband unlocked morotola e680i linux smartphone. this phone is NOT 3g. it works perfectly in tulsa, OK, but in oklahoma city it does not even see any cingular towers much less connect to them. the phone sees tmobile towers in OKC and tulsa both!

from speaking with cingular reps and CS (not that this information is correct), they said that tulsa is a 3g network whereas OKC is not. i went to a cingular store and picked up one of the latest sim cards and the phone could still not see the towers. i had a cs rep tell me i am probably on a partner tower, and i had the sales rep in store tell me cingular has no more partner towers. i do not know the validity to either of these claims.

i've used a tmobile sim card and both tulsa and OKC work perfectly. i've done manual searches with the phone using all bands and each band individually to see what i can pick up, and it is always tmobile towers ONLY in oklahoma city.

not sure what else i can try. any help or insight would be greatly appreciated! thanks.