iPhone App Development on Ubuntu

Many of the other solutions will work, but they all make use of the open-toolchain for the iPhone SDK. So, yes, you can write software for the iPhone on other platforms... BUT...

Since you specify that you want your app to end up on the App Store, then, no, there's not really any way to do this. There's certainly no time effective way to do this. Even if you only value your own time at $20/hr, it will be far more efficient to buy a used intel Mac, and download the free SDK.

Not officially, no. It's just Objective-C though and the compiler's open source - you could probably get the headers and compile it and somehow get the binary on the device. Another option is compiling on the device. All these options will require jailbreaking though.
A Mac Mini is just $599...

There are two things I think you could try to develop iPhone applications.

1. You can try the Aptana mobile wep app plugin for eclipse which is nice, although still in early stage. It comes with a emulator for running the applications so this could be helpful

2. You can try cocoa

3. (Extra) Here is a nice guide I found of guy who managed to get the iPhone SDK running in ubuntu, hope this help -_-. iPhone on Ubuntu

I found one interesting site which seems pretty detailed on how you could setup a ubuntu for iPhone development. But it's a little old from November 2008 for the SDK 2.0.

Ubuntu 8.10 for iPhone open toolchain SDK2.0

The instructions also include something about the Android SDK/Emulator which you can leave out.

With some tweaking and lots of sweat, it's probably possible to get gcc to compile your Obj-C source on Ubuntu to a binary form that will be compatible with an iPhone ARM processor. But that can't really be considered "iPhone Application development" because you won't have access to all the proprietary APIs of the iPhone (all the Cocoa stuff).

Another real problem is you need to sign your apps so that they can be made available to the app store. I know of no other tool than XCode to achieve that.

Also, you won't be able to test your code, as they is no open source iPhone simulator... maybe you might pull something off with qemu, but again, lots of effort ahead for a small result.

So you might as well buy a used mac or a Mac mini as it has been mentioned previously, you'll save yourself a lot of effort.

Probably not. While I can't log into the Apple Development site, according to this post you need an intel mac platform.

http://tinleyharrier.blogspot.com/2008/03/iphone-sdk-requirements.html

It can be done!!!!!!

There is someone who did it.

Enjoy :)