Yes, but this is probably best instituted at the telecom layer as there are fewer people to educate / complain / litigate drama. Telecoms who self-police don't need it and if they fall from grace they can post collateral to be let back in. I predict that suddenly the telecoms who previously turned a blind eye towards scam call-centers will suddenly become very good at pursuing scammers once they become a threat rather than an asset.

> There's still a problem where someone asks to be called (the number needn't actually be theirs) as a way to trick the caller into losing money... But even then, I think it represents an improvement over what we've got now.

That's basically the purpose toll free area codes used to serve; and there's no reason that same sort of solution (with some adjustments for the modern era) couldn't continue to be used under a deposit based system. Just add some universal prefix, some unused country code for instance, that can be dialed for a "no deposit" call; and then give control to the recipient whether they want to accept such calls.

Or, well, since most modern dialing is done by submitting the whole number at once rather than digit-by-digit; it could even be a suffix. If your number is +12125551212, maybe something like +12125551212*0 could indicate a "no deposit" call. I mean, the whole suffix space could even be turned into something akin to a password so instead of just opening up accepting "no deposit" calls from the entire world, you might only accept them from specific whitelisted suffixes; and if someone leaks one and you start getting spam calls on it, you can just turn off that suffix. There might need to be some provider-enforced fail2ban to prevent wardialing those suffixes, but it doesn't sound like it'd be too difficult.