I suppose you could always ignore after-hours calls from work - boss or otherwise - but the fallout would unfortunately have been pretty predictable.
Good news all round. Fuck doing work outside the paid window. Unless it's a dire personal emergency for one of my staff, then fine - but damn right I'm taking a half hour flyer one day in the week.
If they aren't in the contract, and don't get paid at after-hours rates, ignoring them is always the right call. You're either on call, and paid for it, or you aren't. The alternative, is slavery.
On the other hand, if you work remote freelance, "after hours" becomes more of a nebulous concept, with calls and meetings being either scheduled or unscheduled. Unscheduled ones are fair to get ignored for up to 12 hours, with "send me an email" being also a good response.
The problem is, that many employees are not in a position to ignore their bosses. Making it downright illegal to call after-hours is the only way to enforce this.
A few public sector organisations have had a compromise, where you get an hourly rate and a phone to be on-call. It's something daft like two pounds per hour, but it does work out to be an extra £100 or £150 a month before tax with attendance expenses paid if you needed to get onsite.
There was probably a compensation arrangement too but I just took off the time that I worked at my convenience - generally the following day in the morning for a lie-in.