Okay, but my question was not about this phone specifically, but about whether flashing a phone in general with a stock rom will lock the phone back to the original carrier.
Here is my problem. I bought the phone as an "Unlocked" phone. But it came with a custom rom that was glitchy. To fix the problem, I flashed the phone with the stock rom. When I inserted a non-AT&T SIM card, it asked for a network unlock code. Now, if what Funkylogik said is true, that rom flashing has nothing to do with network locking, then the seller I bought this phone from did not actually unlock the phone before sending it to me, all they did was flash it with a custom rom. In this case I need to leave them a scathing review. But if, flashing with the stock rom, does return the phone back to the locked state, then I don't need to leave a scathing, just a bad one because they put a glitchy rom on the phone or at bare minimum did not test the phone before sending it out, and they also did not answer my email for support.