Show HN: Expensive Chat – Pay one cent per letter
It's such an obvious idea, and it has been around for as long as spam e-mail has been a problem.  I absolutely do not understand why it has not yet been adopted for all e-mail traffic worldwide.  If an e-mail were to cost just one cent, it would never add up to an amount that a normal person would even notice, yet it would solve the problem of spam e-mail over night.