I wonder myself. The Galaxy Ace (Which passed my good phone test by not exasperating me to the point of a club hammer test and surviving immersion,) doesn't behave in the air as it hasn't got gyros but a friend has an S2 which seems to work ok. I would envisage a use for it in VFR when crossing the channel, should the haze make the horizon indistinct together with a beady eye on the altimeter and slip ball, naturally.