How to tell if my phone is unlocked for any carrier WITHOUT using another carrier sim

[gtcherer]

AT&T free unlock service takes about a day (unlike most of the paid sites that take up to 3 days). Just go to att.com/deviceunlock/#/ they email the unlock code (with instructions that did not work for me).
also, i got a straighttalk tmobile and an at&t nano sim for 99 cents each online from walmart. i put the tmob in my att phone, punched in the unlock code when prompted, and the unlock magically occurs.