As a google brings about 3 million results. I have a new to me 4,any advice on who I should use to unlock it?

Try contacting three to see if they will do it for you.

Usually it’s the original phone owner who has to get it unlocked.

Phone 3, it’s cost you around £15 which is less than I paid… as mentioned some network will unlock them for the original owner for free (O2 did for me, on another iphone)

Or jailbreaking it.. apparently does it (until you update it with the latest Apple update)

Three again. They’ll do it for 15 quid as zippy said.

I had this with an iPhone I sold. I rang three and paid the £15.00, as it was still under my name with them.