The best mobile operators in Turkey are Turkcell and Vodafone. You are able to use your GSM phone in Turkey if your local provider has enabled international roaming. However if you intend to stay in Turkey or make several calls, it may be preferable to buy a prepaid SIM card. Take your GSM phone and passport to a Turkish mobile phone shop where your new SIM will be registered along with your handset’s IMEI number and your personal information. Our country has very wide GSM coverage networks so you shouldn’t have any problems in the major cities and sites.