age. But they were not mobile telephones; the recipi- ent of the beep typically had to scurry to the nearest pay station to respond to the message. Car phones did exist, but they were very rare. The original car phone sys- tem in the United States was known as MTS, for mobile telephone system; it used full-duplex VHF FM radios and needed operators to place calls. Band- width capacity was very limited; only a few frequency pairs were available in any given city, SO only a few hundred MTS phones could be issued by the local tele- phone company. This was followed up by IMTS (improved MTS), which allowed direct dialing of calls; IMTS phones actually used rotary pulse signaling to dial digits. But that did not solve the frequency availability problem; IMTS phones were generally the province of tycoons and others who could afford to wait years for one to become available. In the early 1970s, two companies raced to be the one to make mobile telephones more available, though neither imagined how successful they would become. AT&T, then owner of the monopoly Bell System local tele- phone companies, sought to make car phones more available than IMTS could be. Motorola, then the leader in hand-held radio manufacturing, set out to make a hand-held mobile phone. In 1973, Motorola's Martin Coo- per made the first call on a 30-ounce hand-held prototype of the first cellu- lar phone, and although the 10-inch-high handset was a bit heavy, further development led to a continual reduction in size and weight. Cooper is widely credited with inventing the cell phone. But it was not just the radio components that mattered. The mobile phones themselves operated under the command of the network, following a complex protocol, shifting frequen- cies on command. Was it entirely a coincidence that Motorola's semiconductor division introduced its first microprocessors just after Cooper's first cell phone was built? The system is called cellular because it divides the network's service area into small geographic areas, each served by a base st