oh just found this
Has your UK mobile been blocked by the recent changes in the Turkish Telecommunications regulations? If so, here’s how to get it working again or make sure it works once you get here.
Registering a Foreign Phone for Use on the Turkish Mobile Network
Show your handset and original invoice to Customs upon your arrival at the airport. They will stamp the invoice. If you don’t have the original invoice they will issue you with a form and stamp that. Hold onto this as you will need it later.
If you didn’t declare it at the airport then you can declare it at your local Customs. You will need to show them your handset, invoice, passport and flight ticket.
Next, (when you arrive at your destination) take a copy of your passport page with your entry visa stamp on it.
Take the two bits of paper (invoice and copy of passport page) and attach them to a letter stating you would like your UK phone to be able to use a Turkish SIM card and why you have been unable to register it so far (e.g. you were out of the Country).
Stick them in an envelope and send to your Turkish mobile phone subscription centre (ask at you local mobile phone shop for the details). They will register it with the Telecommunications Authority.
We expect sometime later that you will receive confirmation that your phone can use a Turkish SIM. In any case you could use your phone and see what happens (sorry that’s about as accurate as we can be on this part of the process).
There is no charge for this process!
If you need to quote the law to any of the officials it can be found at the link below:
http://www.tk.gov.tr/eng/pdf/regulation_amending.pdf
Please make sure you phone is unlocked or SIM Free to be able to use a Turkish SIM card.
There is no import duty to pay if your phone cost less than €300 - approx £200.
Fendlyra