I can't say anything specific about ASA, but with 121 carriers any commercial flying outside of the airline is a no-no. But as far as side stuff- many people do it. Your time off is yours, and a 2 hour call out just requires you be there ready to go 2 hours after the phone call. I have flown with many guys that have side gigs, and I am trying to get one myself. What I have heard the vast majority do is jobs that are self employment things, or things out of the office that you do on your time as opposed to a part time gig with a schedule. hope that helps a little.