I have a Nokia Symbian phone and just started writing code for it using Qt in my free time. Forget about the actual platform though. My point is as follows.
Seeing my code run on a phone is a lot of fun! Sure I used to do lots of things with my phone before (email, web browsing, games, voice calls the usual) and yes I did customize the phone and settings to my liking before, but writing code gives you so much freedom and suddenly my phone feels like an empty slate waiting to be molded into whatever shape I decide to
Suddenly you start thinking of thousands of things you can build with your phone! You go from user or even power user to builder/constructor of stuff!
It is the same feeling I had many years ago when as a kid I first discovered programming for the PC.
So developers, current and aspiring, if you do have a smartphone of any kind (never mind the particular type), do try out writing anything for your phone! It might be a simple to-do list application, a game, to a control-this-robot-over-bluetooth or whatever. Writing for phones is fun so do try it!