There is a booth at the arrival terminal of Istanbul Atatürk Airport. The company is called IUGOIUGO. They are renting wifiWiFi modems, smartphones, tablets and GPS Navigatorsnavigators. DailyThe service became available in June 2014.
WiFi modems and smartphones cost 6EUR/day to rent prices are approximately 3,9 Euro. Here's a photo of the location (sourced from IUGO's official Twitter page):