Beste antwoord door David
How unfortunate that you're not satisfied with your iPhone! :S
By unlocking your phone, you mean making it usable for other sim cards? If this is the case, all iPhones delivered since 2011 are already free of a simlock, thus can be used with other sim cards as well. If you mean another lock, let us know!
Perhaps this is already very logical for you, but I just wanted to make sure that you also completely swipe the phone clean, before selling to another person. :)
If you have any further questions, don't hesitate to ask!