The short answer is that fundamentally iPhone OS uses Cocoa, which is a closed infrastructure distributed only with Xcode. Some people thought about reverse engineering (like Wine), but I don't think anyone really succeeded so far, not to mention using Cocoa as a development environment.
You may be able to create some debian packages (dpkg) that can be run in the background or through a mobile terminal. This is a kind of limitation because you do not have access to the graphical interface and your application will not be very intuitive.
There seems to be a development platform for porting Blender game logic to a full iphone game. You might be able to avoid Xcode this way, but I doubt it. http://sio2interactive.com/
You can run OSX in Virtualbox / VMWare Player, but this is prohibited by Apple.
ejang
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