By the looks of it, Facebook will be implementing friends-to-friends payment in the very near future. Users will be able to send money to their friends by using the Facebook Messenger application, which already has the payments code built in. However, no one is able to use it yet.
This hidden feature has been discovered by Andrew Aude, a student of Stanford University. By using Cycript, which is a helpful application exploration tool for developers, he stumbled upon a piece of code hinting at person-to-person monetary transactions.