Blackberry’s and Unified Messages

We recently purchased a new telephone system that allows for Unified Message delivery to our Outlook Inbox. All seems well there. The problem is that our Blackberry users receive the email…..but no .wav file is there to play? Not sure where the file is beeing stripped. Don’t suspect SPAM filter, etc…
Something to do with handhelds ability to translate the file perhaps? Has anyone else experienced this….and if so….please tell me the fix.
We are running a BES Server, Version 4.2.??
Thanks