A US MVNO, Zact (operated over Sprint), offers a "new service that will give you a whole new level of freedom, control and flexibility. With Zact, you get a whole lot more than just voice, text and data. Zact lets you quickly adjust your plan right from your device. You never have to worry about overpaying because you get a Never Overpay Guarantee. All of your voice, text and data is truly shareable, and you get an unprecedented level of parental control of your kids’ devices with Zact.
See "Meet Zact. The First-Ever Smart Mobile Service" - here.