When I check IMEI.info, it says my phone is unlocked. However, I know for a fact that I had a friend unlock it for me, so it isn't factory unlocked or done by a Carrier.
I'm currently running IOS 5, so it's definitely time for an update, but my phone itself is running perfectly, so I don't see the need to buy one of the newer iPhone models.
I currently am under carrier T-Mobile, and I purchased the iPhone about a year and a half ago, on ebay as a used phone from AT&T, if I recall.
Thanks!
См. статью: Is it safe to update my non-factory unlocked iPhone 4 to IOS 7?