How is that not bitcoin?

I've long been a fan of a "bounty" system -- you attach digital coins to a message, with the recipient specifying how many coins must be attached (maybe higher for voice, lower for email, mid level for SMS). If the message was unwanted (not merely spam, but even just a stupid request), the recipient collects the coins; otherwise, the sender gets them back.

This nicely aligns incentives. If the recipient takes coins improperly, you stop sending him mail.