UA flyer here who will be on a few AA flights and I had a question re: SDC or standby question that i hope I can get answered. I have some upcoming flights in business class (fare code I) and was wondering if AA permits SDC or standby for a different flights on the same day? I assume there is no fee, but do I call 24 hours before my flight and is it a confirmed change if the fare code is available or an airport standby? If standby, does an I fare trump someone using 500-mile certs (I have no status on AA but am considering a status match)? TIA for any help!