There are tons of posts and articles about cross-domain communication and Same Origin Policy limitations on the web, but none of them are providing you a real browser-transparent solution.
After I dug over a month in this area, I have finally found the best solution!
It is called EasyXDM, and I really want to thank to oyvind for it.
I'm not going to write just yet of how easy can it be used but you can read here
There was a bug on the Tests suite that was crashing Google Chrome and Safari browsers but I have fixed it here. Be aware that the tests are forced to run in all the transports and some of them are expected to fail in certain browsers. However all of them should pass on the "Best Transport" tests suite.
[Update: Oyvind has also updated the test suite here]
For those who don't want to spend a month doing the research they can start with these resources:
Enjoy cross domain re-usable applications!