With mobile phone service available in more than 210 countries, blanketing most major cities, you might think rural areas are the top priority for extending wireless coverage.

You would be wrong. There is an urgent need for better wireless coverage much closer to home. In fact, it's inside the home - and all other buildings.

There are now more wireless phone subscribers worldwide than wireline phone subscribers. In developing countries, a mobile phone is often the user's first phone. In developed countries, a growing number of consumers and enterprises are making mobile phones their primary phones.

In other words, what started as a car phone for the rich is now a personal voice/data communicator for roughly one-third of the earth's inhabitants. People take their mobile phones everywhere and expect them to work everywhere - in homes, office buildings, hotels, convention centers and even subways. Outdoor cell sites, by themselves, will probably never provide adequate indoor coverage. Office buildings often contain steel, thermal windows and other materials that attenuate radio signals. Homes can be obstructed by hills and foliage. Plus, high-speed services such as streaming video and downloading games require better signals, so a building with acceptable voice coverage may exhibit unacceptable data coverage.

The network industry is responding to this challenge in different ways, and it will be interesting to see how it plays out. Companies such as ADC, Andrew Corp., Comba Telecom, Dekolink and LGC Wireless are providing coverage inside midsize to large facilities using repeaters and distributed antennas.

The Nextel side of Sprint-Nextel has been particularly aggressive in convincing enterprises to use its mobile phones indoors. Push-to-Talk and Talkgroup features make Nextel's service an especially good fit for enterprise users. The firm works with infrastructure suppliers to ensure coverage throughout a customer's premises using repeaters or micro base stations.

In addition, wireless LAN (WLAN) and mobile phone industries are jointly addressing the in-building challenge. WLAN makers are adding VoIP to their products while mobile phone manufacturers are adding Wi-Fi to handsets. Cellular infrastructure suppliers are developing solutions for handing calls and data sessions back and forth between mobile phone networks and WLANs.