If you're using Blackberry Internet Service, you can login to your Carriers blackberry service site. Under profiles you can add additional e-mails in there so they associate themselves with your handheld. Yes, they are real-time.
I have 3 e-mails associated with my Blackberry.
My business e-mail account.
My main ISP account
and a sub ISP account
All of which come in once they hit their respective inboxes.
Cingular :: BlackBerry 8700c