I booked a late flight for PHL -> LAS on United, but the flight seems to actually be on US Airways. There are 2 or 3 earlier flights that I would like to get on if possible.

From my search it seems I can do a standby flight on United without additional charge, however US Airways seems to charge $25 for this. I don't know which carrier's policy would apply in this instance, anyone know?

It's probably worth the money to get there earlier, but I'm a tightwad .

Also, I'm probably going to hang out in one of the lounges (using priority pass), would I be able to exit the lounge to wait for standby at the gate and return to the lounge (without having to pay again) if I don't get it?

Thanks