Are femtocells just for voice calls or can I also use them for data?

Sprint's Airave, the only femtocell service commercially available in the US today, supports 1xRTT data but does not support high-speed 1xEV-DO data. However, 3G femtocell services will provide high-speed data access in Japan in early 2009 and are likely to appear in Europe soon after, analysts say.

Can I take one on the road with me?

That depends on where you're going. While they're intended for home use, femtocells can be taken on the road (Sprint's Airave box is about the same size as a standard home router) -- provided you're staying in the US and the wireless carrier offers coverage at the new location.

"The Sprint one uses GPS and won't transmit unless its location is within Sprint's territory and Sprint says 'yes,'" Nogee says -- an assertion confirmed by Sprint's Airave documentation (PDF) . Sprint recommends that you check the ZIP code of the area to which you're traveling to confirm that the service is available there.

What's required for setup?

Femtocell devices require you to have a wired broadband Internet connection, such as DSL or cable; they won't work with satellite or dial-up connections. In addition, you must have an available power outlet and a free Ethernet port on your modem or router. And, of course, you'll need a mobile phone and calling plan with the carrier offering the femtocell service.

Sprint's Airave box requires little setup or configuration; however, it must be located near a window for the GPS feature to work, according to Sprint's Airave documentation (PDF) . The global positioning service "can take up to an hour to locate a satellite," according to Ovum analyst Steven Hartley .

Once set up, how well do they work?

Femtocells repeatedly scan the environment, seeking out the strongest signal to optimize the connection. Independent tests of Sprint's Airave from the likes of Engadget and Slashgear found the signal to be strong and clear in areas that were weak or nonfunctional without Airave. BusinessWeek , on the other hand, found the coverage to be spotty.

Once a connection is established, it won't exceed the maximum data rate of your broadband network, experts say -- something to keep in mind if you plan to have multiple callers using the service simultaneously.