As if users did not already have a powerful set of choices for wireless networking, existing terrestrial services will soon be complemented by a number of new satellite based services. Until now satellite communications has required fairly large terminals, ranging from briefcase size to suitcase size to communicate with geostationary satellites located some 36,000 km above the planet. But low earth orbit (LEO) systems now being deployed use a larger number of satellites at much lower altitudes ranging from 500 to 2,000 km. Communicating with these "base stations" in the sky requires much less power, and can be accommodated by handsets only slightly larger than today's cellphones.

These satellite services will offer a combination of voice, data, messaging and location services worldwide. Data services will typically range from 2,400 bps to 9,600 bps for both circuit-switched connections to the PSTN and packet-switched connections to the Internet. Like cellular data services, users will usually have a serial connection between their mobile computer and the handset.

Priced from 50 cents to $2.00 per minute, satellite services will not compete directly with terrestrial systems, but will instead complement them by offering service in areas without terrestrial coverage. A number of vendors are already developing dual-mode handsets that automatically use a terrestrial cellular connection when available but fall back to a satellite connection when in remote areas.

Some of the principal systems include):

• Globalstar. CDMA system with 48 satellites. Service available in 1998. 9600 bps data service.
• ICO Global Communications. TDMA system with 10 satellites. Service available in 1999. 2400 bps data service.
• Iridium. TDMA service with 66 satellites. Service available in late 1998. 2400 bps data service.
• Orbcomm. Service with 28 satellites. Limited service available now. Two-way messaging service.