If you are going to travel in Turkey for a long time, it might make sense to get a Turkish sim-card and enjoy the local mobile network services. You can access Internet anywhere without hunting for WiFi. And also, you will be able do certain things online, like buying an interstate bus tickets, which requires a Turkish cell phone number.

Out of all the operators, I would recommend Turkcell, as it has the most consistent coverage all over Turkey. It offers the following data plans as of 2018:

You get a Turkcell sim-card in any Turkcell office in Turkey, which can be found in most of the airports and city centers.