It's been tried before, usually as a joke. Kids magazines that say "not for sale to adults". Gaming mods that make you pledge your first born to the developer.
To work, the laws of the country the user is in will apply, and will have to be enforced.
Well... in my experience it never went well. Every teenage couple where one or both went to Uni ended up breaking up before the year was out.
SMS was relatively expensive in the 90's/00's, as was broadband - a lot of folk were on dial-up internet, which was also paid by the minute. So if money was a factor you'd go online, download your emails, disconnect, then draft all your replies, reconnect and send.
In fact, email was probably the preferred non-urgent medium between my peers until 2008 or so. SMS was more of a "hey, we're headed to the bar now" kinda thing.
Letters were getting rarer and rarer - but one particular friend I exchanged actual postal letters a few times a year until 2012 or so.
As for family, my mum called me every week, and I never went more than 6 weeks between visits back home. Still don't.
I remember back when it used to be full of experts or professionals talking educated sense about things. Then I noticed the general standard dropping down to about my level of intelligence/knowledge - which is not great - and then sinking ever lower to the point it's barely worth reading anymore.
I think what this shows is that the idea of communism attracts the worst type of people as leaders. They enjoy being in charge of everything about a country, and/or can't believe people don't act the way communist theory says they would act under communism, so kill them for being corrupt traitors in order to fix the system.
As humans in civil society, we're kinda obligated to not do the bad things though. That's the danger with becoming rich and/or famous... I don't believe money corrupts, but reveals our darker impulses, once we feel we could get away with doing them.
Possibly Ghengis Khan too. And a handful of Roman Emperors and European royalty.