Can't get a decent cell signal in your living room? I know the feeling. That's why more and more carriers are offering femtocells: compact, antenna-equipped boxes that use your home broadband network to boost cell reception. Clever idea—although you'll pay extra for the privilege, of course.

Sprint has had its own femtocell device—the Airave—on sale for more than a year now, while Verizon Wireless announced its own femtocell service this week. That leaves AT&T, which is rumored to have a femtocell product in the works, and T-Mobile, which offers something a little different: Unlimited HotSpot Calling (formerly known as T-Mobile HotSpot @Home).

So, how do femtocells work? You can read up on the nuts and bolts at Wikipedia, but roughly speaking, they act as cell network signal repeaters (with an effective range of about 5,000 square feet), piggybacking onto your home broadband network to boost patchy coverage—good news for those of us with terrible reception in our homes and apartments. (I live in a 150-year-old-plus brownstone in Brooklyn, and unless I stand by a window, callers can't hear me.)

The femtocell device itself looks a lot like a standard Wi-Fi router; just plug it into your home network via Ethernet and get ready for more bars. In Sprint's case, its Airave femtocell also comes with a GPS receiver, intended as both a 911 locator and to make sure that you're only using the device in Sprint's coverage area (and not, say, in China or something).

Verizon Wireless is the latest U.S. carrier to jump on the femtocell bandwagon, just having announced its "Network Extender" earlier this week. The box is pricey at $249, and it doesn't support 3G EV-DO data; that said, once you fork over the cash, there aren't any additional monthly fees.

Sprint's Airave femtocell (which uses the same Samsung hardware as Verizon's Network Expander) is way cheaper at $99.99, but you'll have to cough up a monthy service fee: $4.99 a month for "basic" coverage, or $10/month for unlimited Airave calling on a single-line Sprint account (the unlimited charge goes up to $20 a month for multi-line family plans).

AT&T has yet to offer its own femtocell service, but based on this customer survey that's making the rounds, I'd expect to hear an announcement in the near future.

Finally, there's T-Mobile, which doesn't do femtocells at all. Instead, the carrier has a service called Unlimited HotSpot Calling (formerly known as T-Mobile HotSpot @Home, and not to be confused with the new @Home "landline" service), which lets you make unlimited calls over Wi-Fi for $10 a month. (You're supposed to use a special, $29.99 T-Mobile router with the service, but as this review notes, Unlimited HotSpot Calling should work just fine with your existing Wi-Fi network).

Pretty nice—but there's a catch. While any Sprint or Verizon phone will work with their respective femtocell units, you must use one of T-Mobile's UMA-enabled Wi-Fi handsets for Unlimited HotSpot calling. Supported models include the BlackBerry Pearl, the Samsung T229 and Katalyst, and the Nokia 6301 and 7510 handsets—and for now, that's it.

So, who out there would be willing to pay extra for better cell coverage indoors? Or would you rather just stick with a landline?