Fixed-mobile convergence has always been seen in the United States as one of the pawns in the game of RBOCs vs. cable companies. The former were supposed to be looking at FMC to link profitable mobile voice with less-than-profitable wireline voice, the latter as a way of eliminating FMC as an RBOC differentiator and possibly easing their own installation problems.

Now T-Mobile, a player in neither camp, is taking an early FMC position that may cause both RBOCs and cable companies to jump-start their own efforts.

T-Mobile's offering, HotSpot@Home, is based on a new series of handsets that roam between Wi-Fi and cellular services. This means a Wi-Fi voice can be used with a home network or a T-Mobile hot spot. The service is available only in certain areas, but the company expects to roll it out nationally in 2007.

For consumers, a handset that can roam between Wi-Fi hot spots (including a home network) and the cellular network represents a potential savings in airtime charges on their cell phones. You can walk into your home (or another qualifying hot spot), and a call in progress will roam over onto your home network, saving you minutes. You also get reliable reception in areas where T-Mobile has hot spots, such as airport lounges. In theory, it will let you give up your landline for a purely untethered life.

Which, of course, may be why you're getting this from T-Mobile and not AT&T or Verizon. The RBOCs' quarterly numbers have shown declines in their access lines, so you would hardly expect RBOCs to jump out in front of the dual-mode handset trend. The cable companies, on the other hand, have every reason to want to support the kind of FMC T-Mobile offers.