Set Phone to Vibrate
Ooo...call me again

Its kinda annoying to get phone calls when hidden since suddenly everyone becomes subconciously aware that you're there. Why not a vibrate option that only alerts the player?

I think it's more of a player police themselves kinda deal, unless you're in a small area with no ambient population or anything like that, but that's a given.
Of course, alot of people don't police themselves, hey, sometime I find myself doing weird things too, so I'm not pointing fingers. So yeah, Vibrate.