Without wanting to get into it in detail, there are numerous ways of noting the position of a downed aircraft and passing that information on to the appropriate people. One at the very bottom of the list is a mayday call to the airspace controllers. Very very relevant in the event of a peacetime crash back home mind you, but in theatre I think there are things I'd rely on before a mayday call, especially if the airspace frequency isn't always secure.
I don't know who's carrying a smartphone when on an operational sortie, but they do kindly provide more than just a silk escape map and compass!