how do you know if a phone is locked?

I purchased a nokia 3120 off ebay - it's a cingular phone but apparently is unlocked for tmobile use.

I put in my tmobile sim card and the phone powered on to the main screen but it does not get any reception.

Might it be locked? How would i know if it was locked?

Thanks!

 

Anyway, I suppose it would not hurt to try to unlock it if it is already locked?

Here are my stats:

Make/model phone:
IMEI #: 355028004588010 (with slashes: 355028/00/458801/0)
Country the phone is locked in: USA
Provider the phone is locked to: Cingular phone

 

try this code

#pw+049273364715222+1#