ExteNet has figured out a way to make the iPhone work better by using the heating, ventilation and air conditioning (HVAC) systems inside buildings.

Actually, its expertise with HVAC deployments extends across carriers, including AT&T and the other major carriers, so it can help Droids and other devices work better, too.

The HVAC deployments, which are based on ExteNet's patented iDuct product line, use a building's existing ducts as waveguides for RF signal distribution. Chicago-based ExteNet also installs more traditional in-building systems with distributed antenna systems (DAS) where that makes sense. It also supplies outdoor coverage, but it's the indoor deployments that are really taking off as a percentage of its overall business.

The iDuct/HVAC deployments work best in certain types of buildings, such as a high rise with residential living space, says Eric Lekacz, executive vice president of Business Development and Strategy at ExteNet.

"There are certain venue types that really lend themselves to this approach because it reduces cost of implementation, improves time to market," he says. "You actually get more consistent and uniform performance. It gives us another tool that we can give wireless service providers."

A traditional indoor system might be fine for a warehouse with a lot of cleared space, but if a building has a lot of office spaces that are "chopped up," so to speak, iDuct may be a more cost-effective solution. A site like Chicago's Trump Tower, where ExteNet has installed iDuct, lends itself to an HVAC set-up because it mixes residential and office space. Certain hotels and hospitals are other venues where iDuct makes sense.

ExteNet did initial trial deployments between 18 and 24 months ago to learn how the HVAC technology worked; its deployment at the McCormick Place in Chicago was done about a year and a half or two years ago.

Other in-building coverage companies, like CommScope's Andrew, ADC and SpectraSite, which was acquired by American Tower, offer solutions, as well as untold hundreds of smaller companies, so it's not as if ExteNet has a lock on the market.

But it's in a growth mode thanks to the proliferation of devices, carriers' desires to improve in-building coverage and its own reputation. Privately held, the company is hiring more people on several fronts, and it's only going to get busier with LTE on the way.

"The wireless industry has got to go to a microcellular architecture, and you've got to be close to the user," Lekacz says. "At the end of the day, it's physics."