International students can buy a phone in Turkey from one of the local telephone companies and get a Turkish phone number directly or they can bring their phones with them from their home countries. However in order to be able to use your foreign mobile device, you should first register it officially under the Turkish GSM network with your passport before the registration deadline expires. For passport mobile registration period, contact GSM companies.
You should go to the nearest tax office with your passport, IMEI number of your mobile or the mobile phone itself. There you will be asked to pay 138 TL as tax expenses. And then you need to pay 30 TL for the phone's registration in Turkcell, Vodafone or Turk Telekom and finally 35 TL for the Sim Card. Please note that although these are the most recent prices, they may still be subject to change.