A: Apart from taking and receiving calls (or perhaps giving missed calls :P), I'm guessing the top answers would mostly be these (in no particular order):
Taking photos/videos
Playing games
Listening to music
Text messaging
Internet browsing
However, nearly the most innovative and interesting use for phones that I have ever seen, I got to see today in Tifanys. (Sorry about the pic clarity though.)
An idli on a phone .. Awesome! Never even imagined I could use them like that!
So .. Next time you don't have a plate .. Well, you know what to do. :)