Turkey has strict laws about the importation of cell phones.
All phones brought into the country must be registered with the government within 120 days, and after that, must have a local telephone number.
If you would like to have your own cell phone while you are in Turkey, you have two choices:
1. Use your phone from home. Within 120 days you must register it, pay the tax, and buy a Turkish SIM card with a Turkish phone number.
2. Buy a local phone, with local SIM with a new, Turkish phone number
You will need a Tax Number. You will be given one when you pay the tax for your application for the Student Residence Permit, at the Tax Office.