USA iPhone 3GS warranty replacement on Rogers - Unlocked?

[sinktip]

I was in Houston recently and my iPhone 3GS died. Apple store replaced it and handed it back (amazing customer service by the way). The phone works perfectly fine on my Rogers SIM card. I am from Canada and my phone was/is on the Rogers network.
Does this mean that my phone is unlocked? It doesn't say anything about unlock on the phone or in iTunes (that I can see).

 

[Crystal-RX]

You can borrow a sim from one of your friend on a different network, pop it in and see if you can make calls. If you do, then they replace you with a factory unlocked iphone.