score:12
Cheapest
Connect to free wifi in Istanbul airport. You may have to approach a kiosk to connect to Wifi. It is only free for one hour. Use wisely.
Expensive
Enable International roaming for both and just call each other, or SMS to communicate.
Alternate
Make sure the terminal and flight time. When you land, see if the flight is arrived or delayed. At a predetermined time, wait at any of the predetermined facility and ask your friend to meet at the same time there. Once you meet, you won't need mobile phone.
Alternate 2
You can use an app like Briar, which can communicate with devices connected to same wifi. You both can connect to airport wifi, without internet and communicate with each other. (Wifi firewall may block this). It won't work due to network isolation.
Upvote:2
You (and he) can type ur passport number in machine and get free wifi for an hour. I think its more better way than finding solution to celluar phone