Is my phone unlocked?

I bought my phone on EBAY. Seller says it is unlocked.

It is AT and T, HTC INSPIRE 4 G.
I just so happens that I have an AT and T prepaid sim. I put it in the phone and It works fine. I remove the Sim. It says no sim network. but the phone is still functional for everything else. After restart.

I put in a Rogers Sim prepaid card (Canada), and it says I need to put in Sim Unlock Pin. I went to Rogers store, the girl thinks my phone is no unlocked. I tried another MONTHLY billed carrier in Canada, same as the Rogers Sim.