Great article on Mobile Payments from Fast Company:
http://www.fastcompany.com/blog/chris-dannen/techwatch/mobile-payments-are-taking-which-one-use
Also covering Amazon Payments' mobile solution Amazon TextPayMe.
"[...]Amazon's Payments system also has a mobile iteration called Amazon TextPayMe, which allows Amazon members to pay (or request payment) using their Amazon accounts. Just like Zong and Boku, the whole process requires just a few text messages. The same system allows you to search and buy Amazon products with a feature called TextBuyIt, and like Obopay, there's a Web-based equivalent if you don't feel like messing with your phone to send someone money. You can also send someone a gift card using a text message, if you're of the ilk that likes to micromanage your recipient's spending.
Overall Amazon's system is likely the best for most purposes: simple, secure and flexible, and with about as much simplicity as can be expected from something so capable. And chances are you have an Amazon account anyway."
