Kevin Werback writes definitively:
Spam isn’t going away. It’s one of those things that will always be with us, like junk mail or pirated software.
In a few years, perhaps sooner, the spam problem will go away. Spam will be a minor irritant like, well, junk mail and pirated software.
Things will get better through a combination of responses, none of which will be a magic bullet. This will include legislation, enhanced filters for end-user software and ISPs, widespread use of challenge or whitelist mechanisms, and enforceable codes of conduct for legitimate commercial emailers.
Spam solutions that involve fundamentally changing email, such as charging to receive messages, will never catch on.
Just as the scourge of email spam subsides, spam to mobile phones will start to become intolerable.