I think Twitter can really pivot to become the first aggregated MicroPayments platform.

An all-you-can eat option: $10/Month - Read any news, blog, whatnot, follow anyone, tweet to anyone, upload anykind of media

A-la-cart: pay 0.01$ after reading the 140 character summary for full article access, pay 0.05$ for full tweet stream access to some really useful accounts, etc

Free: Every fourth tweet is an ad, You get only previews of articles, and only a portion of the Tweetstream of really useful content.

Twitter can then kick-back some dough to the content publishers.

Twitter maintains and controls the payment info already anyway. If they get ambitious they can hook into buying and selling as well.