At our university we are forced to use PingPing to pay for our lunch. Only by paying using this system will we get a student discount. Whether this is a good system or not is if no relevance here and might be a good topic for another post.
Anyway you have to register an account at pingping.be. What's very interesting is that once you logged in you can also see when you purchased an SMS ticket! This confirms that every sold SMS ticket is stored in a database and they only need your phone number to confirm if a person has actually bought a ticket.
This also strengthens the argument that the codes used in the SMS are mainly a method so the bus driver can manually verify parts of the code. Of course that's an insecure method but increases the usability. If you know how the codes are constructed you can potentially fool a bus driver, but the actual inspectors will be able to tell it's a fake code.