Ideally (and, outside of the US, by law) the employer should set up a rotation schedule for being on-call. 24/7 on-call is toxic as hell, it only works for young singles that don't have any other responsibility than making rent.
Everyone in the team sharing the 24/7 works well for small teams. Nothing sucks more than knowing you are on call an entire night and having to remember not to do anything that may cause you to forget you're on call, become unreachabld (leaving your phone on silent or in another room for hours etc)
