AT&T rolled out its first femtocell device to the public Monday, beginning with a trial run in Charlotte, N.C.

The AT&T Microcell is a mini cell tower that’s designed to boost 3G data and voice signals indoors, using the customer’s home Internet connection. That, in turn, connects with AT&T’s network. It can support as many as four users at once.

So how does it work? The Microcell has a GPS chip that verifies its location during setup. It also has security features that keep it from being accessed by anyone not authorized on your home network.

The cost is $150, but it’s only $50 if you sign up for a $20 monthly plan that provides subscribers within range of the femtocell with unlimited calling. The company says pricing might change if they take the device nationwide.