So limited are the airwaves that engineers constantly look for ways to use them more efficiently. The latest idea is to send digital data over unused cellular telephone channels. Cellular Data Inc., of Palo Alto, Calif., has patented a way to keep the data packets from interfering with voice calls by sending them at low power over narrow slices of vacant "buffer" channels. Now it's lining up cellular system operators to invest in gear so they can offer the data service. GTE Mobilnet Inc. is testing it in Houston.
Cellular Data President Miklos B. Korodi says a network can carry transmissions at up to 2,400 bits per second and could, for example, let retailers verify credit cards in under eight seconds, vs. up to 20 seconds for the standard dial-up method. Other devices that could use the untapped channels include pagers, burglar alarms, and "smart" vending machines that signal when they're empty.