I already pay for unlimited SMS messages in my recurring phone bill, just like I pay to send internet traffic in my digital cable bill and hosting bill. I pay for my gmail account by agreeing to let Google show me ads. I'm already paying to send email.

Micropayments won't rule out spammers. I still get lots of bulk mail in my physical mailbox, and it costs money to send that stuff: more money then a couple cents and it often has a lower response rate than spam. Payments just make the margins smaller, and they'll make up for it by selling better targeted lists.