I ran a 24/7 service organization for a lot of years and the first thing I will say is "critical mass" ends up being 4 or 5 guys if you truly want to get your work done during the day, cover vacations and holidays without killing your people. I do agree, if you are really going to do this you need a duty pager/phone that always gets answered.
Service is rapidly becoming a lost art but our objective off shift was call the customer back within an hour every time and be on site in 2 80-90% of the time. That was actually better than the day shift.
The hourly rate was about 2.5 times the contract day rate.
