The company I work for bills like this:
Normal Call 08:00-16:30 92/man-hour + 75 travel with a 1 hour min (Or something like that)
Emergency 16:30-08:00 175/man hour portal to portal for the tech plus a 150 travel charge.
I go on the clock when the pager goes off and go off when I take my shoes off. We offer customers 24/7 response via a pager that rotates thru the field techs, everybody gets it for a week at a time. The company gives the tech $70/week to carry the pager. The down side is if there is a call pending all day that nobody was able to get to, the on call guy gets stuck with it. Which really sucks when I am working 20 minutes from home but I have to drive past the house to continue into NYC, about an hour (no traffic) away.
