How do I tell if my AT&T iPhone 5 is unlocked? I requested AT&amp;T to unlock my iPhone 5 at http://att.com/deviceunlock . I got an email saying that my device may be unlocked.

According to the instructions in AT&amp;T's email, I need to do an iTunes backup and restore to complete the unlock process.  I have NOT done this yet.

I bought this T-Mobile SIM and inserted it in my iPhone and T-Mobile shows up in my phone's status bar.  I cannot make phone calls because I have not signed up for T-Mobile service and have no intentions to.

So, is my phone unlocked at this point?  Is there something else I can look at to confirm this?

Thanks!
I believe you are unlocked.

I just conducted an experiment for you.  I took my T-Mobile SIM card out of my iPad and put it in my locked AT&amp;T iPhone 6.  It immediately told me "SIM Not Valid. The SIM card that you currently have installed in this iPhone is from a carrier that is not supported under the activation policy that is currently assigned by the activation server."

That is what you'd get if you were locked. Congrats: It seems they did indeed unlock your iPhone.