If each device needs a different frequency, there may not be enough frequencies to go around. Scientists and companies are busily solving the problem two ways. Digital systems allow wave frequencies to carry a greater amount of data. Second, companies are dividing cities into smaller cells. The same frequency can be used in different cells without the waves interfering.
Smaller cells allow one frequency to be reused more often, so more people can go wireless.
In the future we may break up a city into 5,000 cells. The fad won't end. It's becoming a necessity. The wireless units may even become small enough to wear like pins, or on our belts. In 20 states, laws have banned the use of pagers and cell phones in schools.