I have encountered two different situations.
1. A friend of mine has an itouch in Korea. She iMessaged my e-mail address that I added under my "Receive At" in my settings. We were able to message each other totally fine.
2. A friend of mine in korea also has an iPhone 4. She iMessaged me via the same way as above (my e-mail) and her phone number popped up and we were able to iMessage each other totally fine.
So to answer you question, yes it is possible, just make sure you have your apple id set up in your "Receive At" in your settings.
My question regarding this is how does the texting rate apply? Or does it apply at all? I also noticed that whenever 3g or wifi signal is very weak, it turns an iMessage into an SMS. Will iMessage send international messages via SMS if 3g or wifi signal is weak? or will it wait and send it as iMessage? I am just worried at the end of the month I am going to get a huge bill for texting internationally 😟