Don't bother developing for the iPhone.
Yeah it's doing well, but it's still small fry compared to the amount of Windows Mobile, Blackberry, Linux and Symbian devices already out there. In fact, it's not even gaining ground on the latter three.
Despite all Apple's hype and media manipulation they're still bottom of the pile in handsets out there, and Nokia is still extending it's lead by a massive amount month on month. They're only just on par with RIM's sales.
Ultimately the iPhone will hit a plateau though also, they only have one handset line and like the vast majority of the population worldwide if you're not in the brick sized, expensive, finger print smothered handset market then you're not going to buy one of these. Apple can sell to it's fanboys, and it can sell to the odd non-business smartphone users but then what? Just was with the iPod now, it'll start to fizzle out, people will stop caring, and it'll start losing marketshare again. Of course, the MP3 market was relatively new, so it was able to become market leader, the phone market is mature, so any decrease will ultimately lead to Apple being resigned to the history books of the mobile phone markets as their attempt to gain a permanent foothold is forgotten and people go back to worthwhile handsets that businesses and home users alike can use.