They were there, and than gone again. Blocked by government, a lot of tensions between cab services and uber. Evidently. Now they have their license running again but only through regular taxis if I believe. For bigger vans you need 'Black Taxi'. I'm guessing there is an app for that top, or possible through uber even possibly. Uber is not the only mobile application that you can call for a cab or vehicle, there are also Uber alternative applications in Istanbul such as Bitaksi and Itaksi, which are the applications mostly used by locals in need of a yellow taxi.