I agree with your basic point: that this is a problem that's enabled by low-cost telecoms. We already saw that movie, in the 1990s, in Usenet and Email spam. And we know how it ends. Spoilers: everyone dies.
The problem with your proposed solution is that you're going to have an awfully hard time rebottling that genie. We've got low-cost comms. And within the triple entente of costs, infrastructure, and network effects, you're going to see those re-emerge, whether on the PSTN old-school phone network (inclusive of mobile and VOIP), or on some replacement.
Infrastructure, because you're talking about billions of subscribers. Even a limited network is tens to hundreds of millions. (Numbers for online community services are similar.)
Costs, because users will migrate to the low-cost solution, all else being equal. If regulation requires a cost floor on one network, you'll see migrations elsewhere, and legislation and regulation virtually always lag.
Network effects, because an effective and attractive network is either extraordinarily selective (The Harvard Face Book), or universal (Facebook). Much of the actual systemic value comes not from what the vendor or service provider, er, provides, but from what the users bring to the network. And a large network makes up for a lot of crud in other areas.
(Corollary: the replacement service is almost certain to emerge within some elite niche, and then spread out, as did writing, literacy, publishing, telephony, the Internet, mobile phones, smartphones, and social networking.)
(Corollary: alternatives which start out with the spammers and marketers already on-board and running rampant will likely fail to make the cut.)
Increasing costs across the board won't work.
Oh, and you've got a whole mass of vested interests propping up the current system. I've already linked Bernhard J. Stern's "Resistances to the Adoption of Technological Innovations", but the logic expressed there largely applies, and the paper itself includes several comms-based examples.
Increasing costs for malfeasance, most especially at the service provider level, probably through some charge-back or penalty scheme, with (excellent suggestion from, er, you, by the way: https://news.ycombinator.com/item?id=21494014) a bounty available to third parties, could well be part of that.
A basic outline which you'll also find widely repeated through history.
Markets caused this problem through externalities, informational asymmetries, vested power relationships, sunk costs, network effects, and perverse incentives. You're not going to solve the problem by marketing it harder.