I just called the support number for BES at 1-800-327-9085 and was told that the BES service requires an email platform (exchange server?) to be able to do encrypted text messaging? She went further to say that all BB text messaging is encrypted so why have BES if not using their email?
I found the woman to be quite rude - talking over top of me as I was trying to ask a question etc. Any other source of info or number that you might recommend?