Sprint says it will make available mid-month a nationwide femtocell-based service that allows you to buy and install a small $100 CDMA amplifier to boost signals in Sprint's licensed spectrum across about 5,000 square feet of space in your home or office. OK, addressing poor in-building coverage with a simple and relatively inexpensive device is admirable. But there are some outstanding questions about usage, frequency coordination, pricing and other issues.

First, from the consumer point of view: To use the femtocell service, dubbed Airave, you must already have a Sprint voice plan. Personally, I’ve been a fan, in concept, of Sprint’s Simply Everything plan, available since February. The program undercuts the competition with a $99 unlimited plan for all the voice, data, text, Sprint TV, and GPS you can eat without you having to worry about the meter running.

Now let’s say coverage from the Sprint macro-cellular network is inferior inside your home and office, but you want all the aforementioned services to work there, too. You have to spend another hundred bucks for the CDMA femtocell, which plugs into your (presumably existing) broadband router to allow calls to traverse your Internet access connection, plus shell out an extra $5 a month for an Airave service fee. Unlimited incoming and outgoing calls and nationwide long-distance are included for the extra $5. It’s not clear whether this investment extends your data, text, and TV services, too.

But wait. Shouldn’t I already get all these services with my Simply Everything plan? In the words of wireless aficionado Craig Mathias, principal at wireless consultancy Farpoint Group: “Why shouldn’t Sprint install the femtocells outdoors as fill-in cells [to the macro network] instead of making users buy them?”

Good point.

Also, what if your broadband ISP is offering voice service and decides it doesn’t want to carry Sprint voice traffic? “If Comcast says, ‘we’re not going to carry that traffic,’ they’ll just block it,” Mathias says.

Also at issue: Frequency-coordination issues relating to seamless roaming indoors and out. We’ll take a look at those next time.

Joanie Wexler is an independent networking technology writer/editor in Silicon Valley.