use your BIS account from AT&T to send your gmail directly to the BB. like this: How to add / delete email addresses - BlackBerryFAQ.com
The spam bots or whatever can very easily create email addresses on those blackberry.net addresses, simply by going through any alpha-numeric combinations... smith@, jsmith@, ksmith@, etc., and on and on.
I know I have never registered my TMo.blackberry.net address anywhere and I was getting several dozens spams a day, a year ago, until I dropped it.
Register another Gmail account for your personal email, plus if you ever change cell carriers, you aren't stuck telling everyone a new address.