I was a reserve commuter for 18 months. It's miserable. It is a de facto b scale for pay and scheduling. The ONLY good thing about SWA reserve compared to other airlines is you get 15 days off a month.
Agree that it would be better if you lived in domicile, but you still get paid less per day, are scheduling's beotch, and are not eligible for premium pay in a move up, elitt, or a lot of other goodies that line holders get.
The website above has the nuts and bolts of it, but ask anyone who is forced to live with the scarlet R, and most will tell you they hate it.
When I went from sitting reserve to holding a line, I drastically reduced the number of days I work and drastically increased my ability to move days, drop some days, and work extra for more pay. I had a line in May that ended up being 9 days of work. I just added on ad hoc and made a killing and still worked less than I would with a reserve line that paid guarantee.