AT&T is offering femtocells to customers in North Carolina, in its first full consumer trial of the technology, which uses a small cellular base station in a home or office to improve coverage.

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 US 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 US 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.

The MicroCell is esigned 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 authorised user list online.

Calls begun on the MicroCell can shift over to the nearest cell tower when the user leaves home, and the same pricing continues to apply on that call. However, calls begun outside can't move on to the MicroCell when the user comes into range. Almost all data services will work over the MicroCell, with the exception of some location-based services, according to AT&T.

A MicroCell can use any wired broadband connection for backhaul, including cable modem, fiber or DSL (Digital Subscriber Line) from any service provider. However, AT&T recommends using connections with at least 1.5Mb per second upstream and 256Kbps downstream. It does not recommend using satellite broadband with the device. If a customer moves, the MicroCell can move with them but needs to be re-registered at the new address, the carrier said.