Your phone will work with your original SIM card with applicable roaming charges. However, if you want to get a Turkish SIM card, you will have to register your phone. Otherwise, you will receive an SMS from BTK (IT and Communication Authority) and the following days your phone will be locked. You have 120 days to register your phone after your arrival day.
To register your phone, you need to obtain a “Vergi Numarası” (tax number) from a “Vergi Dairesi” (tax office). After you have your tax number, you can register your phone with its IMEI (International Mobile Equipment Identity) number (you can learn it by dialing *#06#), and your passport at the same place. You will pay 1500 ₺ and you will get a receipt. Please check the details in your receipt to see if they are correct, which are the IMEI number, your name, surname and passport number. If there is a mistake you cannot register your phone with this receipt.
You can register by two option depending on whether you have a residence permit or not.
Registration without residence permit:
After you receive your correct receipt, you can go to your mobile operator company store (Türk Telekom, Vodafone or Turkcell), pay the registration fee and your phone will be registered within the same day. Some companies and some of their branches do not register phone for foreigners or might demand an extra fee. It is advisable to go with a Turkish speaking friend to make the process easier. Also, buying a new phone you might use when you go back your home country or a cheaper second-hand phone just to use during your stay in Turkey are your other options.
Registration with residence permit by e-devlet:
You can go to any PTT office and get an e-devlet password with your residence permit card. Then you can log in and register your phone to e-devlet website. In order to register your phone to the system you need to pay your tax in advance with the correct details.