I'm a software developer but I also spend anywhere from 25 to 50% of my time doing application support, taking calls, fixing issues, etc.
I'm not aware of an official number of hours that we are expected to work. I try to work a regular 40 hour work week, but in an average week, I probably do at least a few hours of work from home when issues come up. And I'm on call 1 week a month with no extra pay for that.
When big projects are approaching deadlines, we work as much as needed to meet the deadline. For our last big system implementation, everyone in my department worked about 200 hours in 2 weeks, including one stretch of 36 hours straight.
Luckily, that kind of craziness doesn't happen very often.