For goodness sake keep a log. "On call" jobs often violate state and federal rules for exempt and non-exmpt status. Mileage for the second trip to the office should be compensated in some cases.
I've checked with our Provincial & Federal laws and our "Pager Pay" setup is legal. It should also be noted I'm salaried w/ banked OT and it's my call what shifts and/or how much extra time I work.
In some cases the key is the nature of the leash. If they restrict your travel or lifestyle there may be a problem.
I do keep a log, and get it signed off on by our General Manager. In our company I am the IT department so ultimately, I have to deal with the problems anyways. My general rule of thumb is that unless it's a showstopper, I'll wait till Monday to deal with it, at which point it's back on the regular clock. And when I do go out of town, my office just has to grin and bear it till I get back.