iPhone 4s unlock status

Hi,

I took the iphone 4s from ATT carrier with contract and now i have requested the carrier to unlock the phone and then asked to backup and restore the iphone using iTunes. I did it and didn't received any message saying that it is unlocked.

Now I want know how to check phone is unlocked without inserting the other carrier SIM.

Regards,

Gnanavel Kullu (GV)