I've experienced this on my 8830 after about 72-96 hours of heavy use, but I use mine predominantly for the data service like Yahoo IM, BB Messenger, SMS, Web service, BIS email (3 accounts, not heavy on email use). It generally fails when I try to send out data like an IM using Yahoo, I have found that if I hard reset the phone about once every 48-72 hours this won't happen.

Just my two cents, but I think there is an underlying problem that is already identified and your carrier can help you remedy the issue with the BB Knowledgebase. I have no idea what it is, but it doesn't impact the way I use it so I'm not truly concerned.