I want to build a SyncML parsing library (no UI) which should be able to build up messages based on information provided by the host application, fed in by the library's methods. Also, the library should to be able to do callbacks to methods in the host application.

I want to be able to compile this and have it available on as many platforms as possible: Windows, Windows Phone 7 OS, OSX, iOS, Linux, Android, BlackBerry. Basically as many platforms as possible.

The priority is to have this available on mobile devices.

Questions:

1. What setup should I use? (programming languages, compilers, IDE etc.)
2. How would I compile this library for these different platforms and how would I connect to it?
3. Any other info? e.g. articles that cover the subject of cross-platform development?

I haven't done this sort of a cross-platform project before, so any available information to put me in the right direction would be welcomed.

Myself, I have a background in C#/.NET and Objective-C.