Yes – providing your phone is international roaming enabled.
The 3 main GSM operators in Turkey are Turkcell, Avea and Telsim and all GSM operators have roaming agreements with international operators, but remember to check with your provider regarding the actual roaming costs.

If you intend to stay for a while and / or expect to be making a significant number of calls whilst in Turkey you may consider purchasing a local prepaid line to use during your stay. These can be purchased form one of the many mobile phone shops and “topped up” as required by purchasing credits (Kontor Kart) from newspaper booths, grocery stores and many other outlets, you could make a significant saving.

Generally speaking, mobile phone coverage throughout Turkey is very good – there may be some problems in some of remote or mountainous areas though. Also remember that even though you are dialing a local number from one of the local GSM Networks the number you dial must be in the full international dialing format.
I.e. the number should be prefixed by 00 90 and you should drop the first 0 from the area code of the number you are dialing.