My first on call job I had programming call centers for a major company. My basic job was manning the hotline during the weekday from 6am-3pm, doing tickets, and whatnot. The rest was being on call which was shared for a week between 5 people. Every week, there was one primary, and one alternate. The primary from the following week was the alternate for the next week, and so on. It came out that you were only on call 2 out of 5 weeks, and that was fine.
Until the politics came into play.
After about a year, one person "graduated" to a new position where he wouldn't have to be on call. Another person left the company, and was never really replaced. So now I was on call 2/3 weeks. In theory. The other two people were very lazy. One of them was some Orthodox religious person who seemed to have major holidays and festivals about twice a month where she could not be on call and she'd "trade weeks" with one of us, but never really did more than say she'd take "next week, for sure." The other was a kind of a nightclub-hopping single "ladies man" who dressed sharp and partied hard. Even when he was on call, he couldn't hear the pager or would take hours to reply.
My boss just rolled over, because she was afraid they'd pull some EOE stint, and she was sort of passing the time until she left on maternity leave. So I was unofficially "on call" 24x7 for about half a year. I got paged about 2-3 times a night, on average, with jobs that went from a 5-10 minute fix to some that lasted many hours. I got no extra pay, and when review time came around, I got a 3% raise. I was making about a third of the wages of someone else in my position, so she pulled the "well, you're not perfect enough for industry standard" card. My response was to quit.
For up to a year afterward, I still got a few calls a month from the former clients, vendors, and business partners. Most knew I didn't work there anymore, but, "Pleeeeeaaaaase, can you fix this? No one is answering the pages!" No.
In other jobs, I was compensated with unofficial "comp time," and sometimes a cash bonus as a kind of "thanks for covering our ass." Comp time works like, "You worked all night fixing that?" Pfft, don't come in tomorrow, or "I am adding an extra vacation day you can use in any way you see fit later."