There is one project, called XML Virtual Machine, that does sth similar to what you are asking. I was interested in that before i got to know the Objective-C. As far as I knew, cross compiling from Java to iPhone was possible(with some limitations). Project is still in development.
You can checkout its webpage at XML VM webpage.
Maybe ppl from XML VM could answer your question(if they plan on creating cross compiling from Objective-C to Java).
But I still claim that making the application twice(for each platform using different languages and tools) would definitely give better results.
