Sim locked and unlocking on straight talk

Are you referring to Carrier Lock:- Request your iPhone’s original Carrier to unlock your iPhone and if they agree and do it, then you may know the further process here --> How to unlock your iPhone for use with a different carrier ...

PUK? Contact your carrier. Read for more...

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).