You probably use a cell phone operating on a plan supplied by a large carrier, allowing you a certain amount of network usage a month. Or maybe you have an unlimited plan. Either way, you’re probably paying quite a bit for the privilege. Today, a new service provider, Zact, launched as an overlay of Sprint’s network to allow customers extremely granular control over their cell phone plans from within a traditional mobile app. The app requires a great deal of OS integration, so don’t expect to use Zact with an iPhone in the near future. The best part of Zact’s service is the realtime control (from the Zact app) of the phone’s access to the network, allowing remote shutoff of any app’s data access, and on-the-fly purchases of texts, minutes of talk, or data. All of this is paired with a “pay for what you use” ethos that will issue refunds of the value of any unused purchases, even with purchases of unlimited service. It will be interesting to see, with its deep OS integration, if Zact will enter the ad sphere, offering extremely immersive ad experiences as a part of certain service tiers.