When I've been involved in a "developer on call" arrangement it's been nowhere near as arduous yours sounds - we were supporting users of our software but not a

When I've been involved in a "developer on call" arrangement it's been nowhere near as arduous yours sounds - we were supporting users of our software but not an online service, so "help, the central server has gone down!" was less of an issue. We had an informal rotation in the dev team so there was always a named person who'd make sure any customer issue got an intelligent first response - up until a certain point in the evening. That was to ensure we were able to ask for data we needed from customers in other time zones, then look properly when the team were in the next day. I have known people on 24-hour call in companies that had infrastructure that was critical to their business (i.e. "as a service" sort of deals). (personally, where I see developers are already doing some out-of-hours support work voluntarily, I think overformalising would put people off and be counterproductive)