Do I need to unlock my phone to use Consumer Cellular?

Question

I bought a used Iphone 3GS that was an AT&T phone and I was planning to use it with Consumer Cellular who said that I wouldn't need to unlock the phone to use their service. When the phone arrived it worked fine, I didn't have to go through any activation, it just went straight to the home screen. After inserting a SIM card and calling to activate it, the phone continued to work and I was able to text/make calls. Then it said it needed to be updated so I plugged it into itunes and let it be; when I checked on it it had restored itself and now I can no longer get into the phone. All I get is the activating phone screen and it won't recognize my SIM anymore. I bought a new SIM to see if that was the problem..still won't work. Why would it work one minute than just stop? Does this mean that I do infact have to unlock the phone to use it with my new service??

Answer 1

The used iPhone you purchased was apparently jailbroken to unlock it, and restoring iOS removed that jailbreak and your iPhone locked back to AT&T. Only AT&T can unlock it, assuming that the jailbreak hasn't rendered that now impossible as can happen. Here are AT&T's official requirements and procedure for unlocking an iPhone:
https://www.att.com/deviceunlock/client/en_US/
Note these terms in particular:
The person requesting the unlock must be one of the following:
• a current AT&T customer
• a former AT&T customer who can provide the phone number or account number for the account
so you may not be able to get that iPhone unlocked.
Regards.