Sue Mac, I use my Turkcel Vinn in the UK, I use 3G Store, no need to unlock, I purchased the sim and now purchased Gb online when I need it. I used to pay for Gb in Turkey through my Garanti account.
I celetaped the Vinn mobile number inside the back cover of the gadget, when I want to top up in Turkey I take the Vinn to any shop show them the number, tell them how many Gb I want, I get a receipt with the amount paid. when I get on line and check the messages in the account I get confirmation there too.