Agree with comments above regarding cabin crew not understanding what a GPS is or how it works.
I've had a pax tell the cabin crew to tell the flight deck how impressed he was at my 'route so far PA' as he had been monitoring our progress on his GPS. I always make sure that my 'current position PA' is correct but have heard some guys 'wing & a prayer it' & give a standard PA even though we've been flight planned a different route. Won't seem so professional if a pax has a GPS on them.
Let that be a lesson to us all, the punters are getting wise!