i need unlock codes for a nokia 3120

hello, i've been looking all over the internet and calling cell-phone companies, but no one can seem to find the codes i need..
i have a

NOKIA Model:3120b Type:RH-50
IMEI: 353783003162348

please if anyone knows the code for this phone or where i can get it let me know!!

 

Country and network locked to?

 

in the US, it used to be cingular, we are trying to put a t-mobile sim card in it