Airbourn gps aims to acquire 4 satelites to triangulate lat, long positions and also altitude. Ground based gps such as cell phones obviously dont require altitude hence will acquire 3 satelites.
I don't think that is true. Three satellites will fix your position and therefore will give you altitude (although remember this is altitude above a notional earth surface). You need the fourth satellite to resolve the time. Without knowing the time, you can't use GPS. If you had an atomic clock, you'd be alright but without one of those handy, you need to get an extra satellite so the GPS can work out what the exact time is.
Of course, typically nowadays your GPS is magically picking up way more than 4 satellites, and thereby averaging out errors.