The option, which AT&T calls MicroCell, became available to consumers in some parts of the city of about 630,000 on Monday, according to AT&T spokesman Mark Siegel. The MicroCell is designed to be connected to the consumer's broadband service and then start handling all the calls and data sessions within the home from that user's cell phone.

Femtocells have been tried or sold by many carriers in the U.S. and other countries but are still an emerging technology. They can improve in-building coverage, which may be limited by location or type of construction, but also ease the burden on the mobile operator's network. Femtocells may both reduce the number of calls that have to be carried on a given outdoor base station and stave off the need for fatter backhaul connections from cell towers.

"You're seeing exponential increases in the use of wireless data and uses of the network that people never imagined a few years ago," Siegel said. AT&T is responding to that change and trying to offer customers more choices, he said.

AT&T is the second-largest U.S. mobile operator, with 78.2 million customers and an exclusive deal to offer its service on the hot Apple iPhone. But some iPhone users have complained that the sleek device doesn't do as much as it might because of poor network coverage.

In the Charlotte trial, AT&T is gauging consumer response to the MicroCell and to possible pricing plans for the device. There are two pricing plans being offered in Charlotte, Siegel said. One prices the MicroCell at US$150 and makes no change to the customer's monthly plan, simply boosting the coverage in the home. In the other plan, AT&T provides a $100 rebate on the price of the device and charges $20 per month for unlimited domestic voice calls made through the MicroCell. The offering is only for postpaid customers.

The MicroCell is designed to provide coverage over an area of about 5,000 square feet. A customer can grant access to the MicroCell to as many as 10 other phone lines, and no other devices in the area will be able to use it, according to AT&T's frequently asked questions page. As many as four devices can use the MicroCell at one time. Users can manage the MicroCell and authorized user list online.