It's been three years since I was on call, but ours (280-bed county facility) was:
** A minimum rate for carrying the pager (for example, $3.50 an hour)
** Two hours' pay for getting called in every time you got called in (even if you were paged while you were on your way in, and the case got cancelled)
** Time and a half for the first four hours, from the time you arrived at the hospital to the time you left after the case.
** Double-time for any time worked over and above the first four hours.
Hope that helps. I like the phrase "fair and equitable."