SIM Locked on iPhone without carrier

If it was your phone, you paid your carrier every month for many months. Surely you can remember who you paid every month for many months, correct?

If you can't, surely you can narrow it down to only a few possibilities and call the carriers to find out if the phone was locked to their service.

Sorry, but there are no shortcuts or workarounds here.

You will not be able to unlock the phone until you find the carrier that you were using and ask them to unlock the phone.

If you forgot or don't know your SIM PIN

Never try to guess a SIM PIN or PUK code.* The wrong guess can permanently lock your SIM card, and then you would need a new SIM card. If your device asks for a PIN or code that you don't know, here's what to do:

1. Contact the carrier that gave you the SIM card. If you aren't sure which carrier to call, remove the SIM card and check the card for the carrier's name or logo.
2. 
3. Ask your carrier to help you unlock your SIM card using the default SIM PIN or PUK code. 
4. If you can't unlock your SIM card using the SIM PIN or PUK code or if an alert says, "PUK exhausted," ask for a new SIM card.

*If you enter the wrong SIM PIN too many times, your wireless carrier might be able to give you a Personal Unlocking Key (PUK).