I have the same sort of question.
I just moved to the UK from the US and would like to continue using BB Messenger with friends in the US. I have asked several service providers here if I will be able to messenger to the US and have been told no. Maybe I just can't take no for an answer, but I feel like they are wrong. That doesn't seem to make sense.
Assuming I switched from US TMobile to UK TMobile, shouldn't I be able to BB Messenger to US Blackberrys?
And the real question of the hour, would there be extra charges because it's international???
Thanks for the help!