How Do I Verify "Factory Unlocked"?

[itags.org]

How do I verify if an iPhone 3GS is truly factory unlocked? I have two that are allegedly "factory unlocked," a 3G 16GB and the 3GS 32GB. I activated the former and got the iTunes message, "Congratulations, your iPhone has been unlocked." Does this alone confirm if an iPhone is factory unlocked? I have yet to activate my 3GS because I want to check with you experts first on the matter.http://images.itags.org/userspace/1/200908011159520457.gif

[dadidoe]

Well, simply insert a SIM Card from a different provider.Here in the UK, my iPhone is locked to O2-UK, so in my case I could test the unlock by inserting a T-Mobile SIM.Since you're in the USA, AT&T is responsible for the iPhone. So try inserting a Verizon SIM Card and see if it works!

[fryke]

Verizon doesn't do GSM, no? T-Mobile would be the test.