If you're a fan of prepaid, Metro by T-Mobile is one of the better options that you can take a look at. If you want to take advantage of its service but want to pay even less (or possibly nothing), the carrier's new collaboration with Ad It Up makes that possible.

The next time you play a game on your cell phone, you might just be paying your bill instead. Ad It Up is a popular app that lets users earn points by playing games, answering surveys, watching videos,