Istanbul’s telephone service has two area codes, one for the Anatolian side and one for the European. If the landline you need to call is on the other side, you must also include its area code 0216 for the Anatolian side and 0212 for the European side. 

Turkey’s country code is +90. International calls from Istanbul can be made from call centers or public telephones using phone cards. If you are going to be making frequent local calls, it is advisable to get a telephone number from a GSM operator. GSM Operators in Turkey such as Turk Telekom, Turkcell, and Vodafone support international calling as well.