In my prior job, I was on hourly, and if I had to answer a work-related call or e-mail, it went on the clock. I just had to e-mail HR and they would log the time. I then presented the call log from the cell phone or the relevant e-mail, for documentation, and got paid for that time.

Went onto overtime many weeks because of that.

I'm currently on salary, and my boss and I keep a running tally in our heads of off-hours projects, and I periodically take a 3-day weekend to catch up from it. Nothing formal, but it works well enough. I don't keep track of the 1-minute calls, and he doesn't keep track of my lunch breaks. It's pretty fair and very reasonable. Neither of us abuses it.

One company I worked for had as many people as possible on salary exempt, and demanded that they do a full 40-hour week every week (or docked their pay), but didn't pay overtime or comp time or anything if they went over 40. Unsurprisingly, that company had amazingly low employee loyalty and had real trouble holding on to anyone with any competence at all. They went bankrupt a while back and all their assets were bought out by competitors.