My company is strictly 8-5 M-F, but of course we have to keep email, Web, and database servers online 24/7. My staff and I are "on call" all the time, with a "phone tree" sort of system for people to reach us if there is an "emergency", usually something like a power failure or "I can't get my email!". We are all salaried, so there is no OT. Any time spent on actual calls is rounded up to the next hour (I actually take into account the circumstances and will round it up even more for my staff) and is paid back as comp-time. The advantage of a "phone tree" is nobody has to work vacation or family time around an "on call" schedule, and nobody has to be tied to a cell phone or pager for any length of time. We just make sure that at least one person in our department is always available. It isn't a perfect system, but it works for us.