This is an extract from Riviera News and the information source is the Turkish Embassy in London.
A young Turkish woman who works in Germany found on her return home that her mobile phone bought in Germany would not work with a Turkish SIM card. The reason is that the Turkish telecommunication industry assigned a unique code (IMEI) to all registered mobiles earlier this year and from now on foreign mobiles will not work with a Turkish SIM card. (This new policy makes trading in stolen phones more difficult.)
So for people who spend a lot of time in Turkey and want to use their foreign mobile with a Turkish SIM card this is what you need to do.
Declare your mobile to customs on arrival in Turkey with the receipt/invoice of the handset. Customs should stamp and date it. (BEWARE: if your phone cost more than 300 euro you will have to pay customs duty on it!). Then to get an IMEI number, go to the nearest Turk Telecom ‘Abone Kayit Merkezi’ – there is one in most towns. There you will need to submit :
The handset receipt with the customs stamp.
A copy of your passport (entry visa page and photo page).
A written petition (this will probably have to be in Turkish) stating that you wish to use your phone in Turkey and want to register it for an IMEI number. Sign it in front of the Telecoms personnel.
To check if your phone is registered press *#06# and if registered your IMEI number will appear.
Please note that this does not affect foreign mobiles which have a foreign SIM card. These will work as normal with roaming function