In Finland companies pay for on-call support time. That is you get extra pay to be available in 15 minutes or whatever timeframe agreed. And really that sort of commitment should not be free.
I used to have such an arrangement, but that was far more stressful.
I’m far happier with the “call me and If I’m able to I’ll answer” approach. I’ve had 2 call outs in 4 years, at a 4 hour cost a piece, both sorted with in 20 minutes.
By charging that 4 hour fee it means the person making the call has to justify it.
If I’m in an offical “on call” situation that limits me - can’t go to cinema, can’t go underground or on a plane, can’t got to the country, because I have a contractual agreement to be on call. Forget that.