I've had a couple of times when I've been called in on a Monday. Once was moving into the theatre, setting up for tech: as ASM, it was important to me to be there, so I felt on top of things/ahead of the game. Got paid 7th day rate. Was given an option not to go if I didn't want to. Another time was for a meeting: I told them that on top of the overtime I would also have to charge for gas and travel time, since I lived ~45 minutes away from the theatre. Interestingly enough, they were able to find time Tuesday morning to have the meeting. It was sort of one of those things where a "higher up" (ya know, the people who have 2 days off and who get paid a heck of a lot more money than me?) didn't want their schedule "incovenienced". I think they knew they were wrong to ask for the Monday meeting.
I'll take calls on a Monday (ie. I let it roll over to voicemail and if I feel that it really is important enough to deal with on my day off I'll call back). If it becomes something that is clearly going to go on for some time I'll hand it off: one Monday I had a prop master call frantic about the fact that the designer hasn't been getting back to her and she needed an answer TODAY. I called the designer (*I* had no trouble reaching him), then the director got involved, finally had to call the Prod Dir because it became a money issue... At this point, it was clear 1) that I really didn't have any decision making power, I was just facilitating 2) this was going to go on all day, so I told the Prod Dir as much and asked him to handle it. He was sympathic, took care of it and left me a phone message later to let me know how it all settled out. It was more than I wanted to do on my Monday, but knowing the folks involved, I may have been faced with the disaster on Tuesday.