Mobile signals often have difficulty penetrating massive steel high-rise buildings, but in Washington's downtown, matters are worse due to height restrictions that force builders to add multiple basement floors.

One law firm knew that a new headquarters near the White House might pose problems for 500 lawyers and staff using wireless handhelds, so it commissioned a site survey before the headquarters was finished that found the mobile signals would probably be poor, especially for a new law library three stories underground.

"Indoor mobile coverage is a real problem in Washington D.C., and we're one of the few tenants to get to a solution," said Rodney Carson, director of administration for the D.C. headquarters of the US law firm Kirkpatrick & Lockhart Preston Gates Ellis LLP.

"The mobile phone companies have not been real forthcoming in solving these problems."

Indeed, two hotels operated by Marriott International at the Grand Lakes resort in the US state of Florida had to install special indoor antennas to boost mobile signals for its guests, several years after the hotels opened.

Carson's law firm started researching the indoor mobile problem in early 2006, and by April had finished installing a system to boost mobile signals for both US based carriers T-Mobile, provider of Research in Motion's BlackBerry service, and for Verizon Wireless, the carrier that the majority of mobile voice users at the law firm rely upon, Carson said.

Carson asked Glasgow Group in Washington to recommend vendors to boost the mobile signals, and the law firm eventually chose LGC Wireless. LGC installed a system of cables, three communications hubs and 24 remote antennas as the new 11-storey high-rise construction was completed.

The LGC InterReach Unison system cost the law firm about $US80,000, while the law firm also paid T-Mobile about $US20,000 to install a mini base station, and Verizon was paid about $US50,000 for a rooftop antenna.

At the Marriott hotels in Orlando, Mobile Access Networks installed special distributed antennas to handle mobile and Wi-Fi, and the total of all the related costs topped $US2 million.

Carson said today that the mobile signals now work well, even in the law library located three storeys underground, where about 60 people work.

"We had all sorts of complaints about the signal at our older building, and with three floors underground, we knew we faced life safety issues, and needed some sort of solution," Carson said.

"Now we get rave reviews from users as well as clients and attorneys from other firms who can get a signal but say they can't get their phones to work at their own offices," he said.

The law firm also has Wi-Fi service throughout the new building, but a decision to add voice over the Wi-Fi has been delayed as IT staff consider security issues, Carson said.

Carson said he realizes that the costs for the project were much less because the work was done during construction and not afterward, as was the case at the Marriott hotels.

Having reliable indoor mobile access is going to prove to be a sound decision, Carson added. "That's especially true because everybody has gotten more reliant on handhelds," he said.