I would suggest getting your hands on the latest iPhone SDK and a Mac from a friend before taking the plunge unless the $600 minimum investment for a macmini(what I did in my case) doesn't bother you.
You could try installing GNUstep for Windows and messing with Objective-C without buying a Mac to check out the language but it's not the same without XCode and Interface Builder,SDK,etc.
The reason I say this is because I'm currently taking an iPhone class and just learning Objective-C is a lot larger learning curve than I thought it would be and eating up a lot more of my time than I cared for.
Unlike C# or Java you have to manually keep track of memory management which is really annoying and a hassle not to mention Cocoa Touch, which is sort of like .Net or Java classes for Objective-C; another big learning curve! Bottom line neglecting the fact that it is a mix of SmallTalk and C and looks horrible if you can get over that it is still hard and easy to crash your program.
Forget to hook up your outlooks correctly in Inteface Builder?
CRASH!
Forget to use an @ for an NSSTring due to the loose type checking?
CRASH!
I'm just saying that you'd probably be more productive and actually get applications completed in your spare time going the Android more familiar Java language route vs the Apple route. Also, I'm not sure how big Android is on the whole MVC concept, but it's everywhere in the iPhone SDK since Cocoa uses the Model-View-Controller (MVC) design pattern throughout.
On the other hand, if you like a challenge or learning the Apple route is the way to go and if you are good you app will sell and you will make money. Like I said there is a ton to learn with the iPhone before you can even start thinking of selling the next killer app LOL.
p.s. Oh and unless you want to test something on actual hardware that doesn't work in the iPhone/iPad simulator or actually upload an app to the store you don't need to pay the $99 fee to develop.
