Nothing... well e-mail, but that's as good as nothing if I'm out of the office.
If I were out the office when something went horribly wrong, I'd expect at least one of my users to do the dutiful thing and call me on my cellphone to tell me they can't do their work. If I didn't get any calls, then I'd just assume the problem wasn't important enough for me to worry about until I got back in.
In other words...
My employers are too cheap to buy me a goddamn BlackBerry! Even when I have a fully functional BES at my disposal! :|