How do single-mode femtocell-based services, such as the forthcoming Airave service from Sprint, stack up against fixed-mobile convergence (FMC) offerings?

Sprint said last week it would make nationwide Airave femtocell service available mid-month. Meanwhile, T-Mobile is also said to be working on a similar service that it will call T-Mobile@Home. Both services make use of the cellular network only.

The emerging femtocell option is aimed at those who live and work in places where the macrocellular network coverage isn’t too hot and who have single-mode cellular phones. You buy a femtocell about the size of a Wi-Fi access point to boost signals throughout your home or office. Sprint’s femtocell price is about $100.

Meanwhile, T-Mobile has already offered a nationwide FMC service called Hotspot@Home for about a year, which combines Wi-Fi and cellular technologies for users of dual-mode phones. Similarly for dual-mode phone users, FMC enterprise-class equipment from companies such as Agito, Aruba, Avaya, Divitas, Nortel, Siemens and others allow you to roam seamlessly between your internal Wi-Fi network and cellular network.

FMC capabilities can be used to overcome poor indoor cellular quality or simply to avoid in-building cellular charges if a private Wi-Fi network is already in place. FMC users, of course, must have dual-mode cellular/Wi-Fi phones.

So what the argument boils down to is this: Should you use one wireless technology or two for indoor and outdoor mobile coverage?

So far, there are a couple marks against the single-mode femtocell approach. It doesn’t appear that roaming from indoors to outside and vice versa will be available. You’ll pay extra, both in capital and a premium on your monthly service fee, for the femtocell service. But you’ll have to reestablish calls when you roam indoors from outside and vice versa – at least in the near term.

On the other hand, FMC products allow you to take advantage of your indoor Wi-Fi network and roam to an outdoor cellular network without dropping the call.

It’s also not clear yet how femtocell services will apply to businesses. For example, Sprint’s Airave service is said to work “in the home or office.” Each Sprint femtocell boosts signals across about 5,000 square feet of space. Could a business purchase 10 of them for a thousand bucks and extend coverage indoors without the need for a distributed antenna system and more expensive micro-cellular base station? Perhaps – but how does this work with the company’s existing set of rates and services that have already been negotiated?

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