At the same time, however, there are new options for how neutral host systems are built and operated, and by whom.

A good example of a neutral host system is now up and running in Chicago's mammoth Sears Tower. The 110-story skyscraper, which covers 3.5 million square feet of office and retail space, houses more than 100 companies. It recently underwent a communications and building automation upgrade that included a neutral host cellular system built and operated by Richardson, Texas-based InnerWireless.

The resulting system supports not only cellular communications but also 2-way radio, Wi-Fi and emergency services communications. That installation reflects InnerWireless' mantra: Wireless communications should be considered a utility with one centralized infrastructure, as with heating and ventilation and basic power systems. Moreover, it is a utility the building owner has as much responsibility to provide as the wireless providers, according to InnerWireless CEO Ed Cantwell.

"We fundamentally believe that for the same reason there are not two sets of plumbing or three sets of HVAC or four sets of electrical wiring that wireless carriers alone don't and can never go build their own infrastructure in these premises," he says. "They can try … They can do a handful. But it can never be a viable industry segment unless the premise owner steps up and plays their role in the distribution of RF within the building."

In the past, carriers focused more on buildings owned by one corporate client as a way to keep a lucrative enterprise account. But that may be expanding to include multitenant buildings such as the Sears Tower. With more than 8,000 employees and visitors walking through its doors 10 hours a day, five days a week, it can justify a carrier's in-building investment, Cantwell argues.

"The Sears Tower alone is bigger than most rural cities," he notes. "Imagine 8,000 people packed within 200 feet of the core of that building. Do you think carriers are interested in that? They will be if they have an efficient way of delivering the signal."

And that interest increases if there is a less-expensive approach. Piggybacking on one central cellular repeater backbone within a building can cut each carrier's installation and maintenance costs significantly compared to a one-of project.

"Instead of building a half-million dollar macrosite, they put a $25,000 microcell in," Cantwell says.

It may be a matter of cost savings beating out competitive rivalry. While competitors in all other aspects, carriers are seeing the benefit to cooperating on in-building systems "because they can split the capex amongst themselves rather than having to pay a neutral company to do it or foot it on their own," says RBC Capital Markets analyst Jonathan Atkin.

Building A Case Neutral host systems also offer benefits to the building owners, and there are signs they are warming to the idea.

"For an enterprise, they certainly would rather have one system go in once, rather than have AT&T do it in February and Nextel do it in April and Verizon do it in August. They'd rather just get it all done. Certainly there is a speed and convenience issue that argues for carriers partnering amongst themselves," Atkin says.

Cantwell also notes this trend, saying building owners are increasingly fueling Inner Wireless' business.

"But you've got to make it work," he says. "You've got to show them the value."

One way to do so is in pairing up cellular upgrades with larger building automation and broadband wireless systems that also can save building owners money, according to Magnus Friberg, CEO of LPG Allgon, a provider of neutral host equipment and systems.

"I think that's a trend," he says. "Some of these systems can be fairly expensive, if you have to pull in fiber or whatever cabling. So in order to get economies of scale, you probably want to have several applications on the same system."

In New York, new regulations also may open the door for neutral host cellular systems. In response to the Sept. 11, 2001, terrorist attacks, the state of New York passed a law requiring buildings with more than 30 floors to install in-building public safety systems.

"If they are going to put in an in-building system for public safety, we think the smart thing to do is to have one common system that can handle public safety. It can do voice and it can also do data," Friberg says.

Taking Ownership But as neutral host systems rise in popularity, how they are built and operated may also change. In the past, third parties typically built and maintained a neutral host backbone, much as with outdoor cell towers. These days, carriers are opting to join forces, working directly with the building owners to install the central system owned either by the carriers or the building owner. In both cases, carriers maintain ownership of their repeaters.

Inner Wireless offers both options, either acting as an intermediary between the building owner and carriers or supplying the gear while leaving the arrangements up to the building owner, Cantwell says.

Allgon also sees both ownership options. For example, it provided neutral host gear for an upgrade project at San Francisco's Moscone Convention Center that was overseen by Inside Wireless. In that case, Inside Wireless owns and operates the system, while the carriers own their individual repeaters.

On the other hand, Allgon also is installing a system for Microsoft's Redmond, Wash., headquarters, in which the software giant will own the gear.

Friberg adds that although the carriers appear to be more open to these ownership options for the neutral host backbone, they also want to make sure their own repeater gear is protected.

And while business is good for neutral host systems, LGP Allgon isn't looking to expand its presence to include managing or operating them for the building owners.

Wariness of the third-party operator model may prove a better long-term strategy given recent trends, according to Atkin. "The neutral host services model for in-building seems to be on the decline," he says. "Carriers would rather deal directly with the building owner and cut out the middleman. So what you find is carriers on an ad-hoc basis partnering amongst each other and dealing with the enterprise or the landlord."

One way or the other, it appears neutral host systems are producing a stronger signal for carriers, building owners and ultimately, wireless subscribers.