The two biggest reasons for running out of numbers within an area code are new technologies and new service providers. (No, we are not experiencing a population explosion.)

New technologies such as fax machines, cellular telephones, pagers, and modems have greatly increased the demand for phone numbers. In the old days, one phone number was enough for an entire family. Now a household could easily use half a dozen numbers.

New service providers also use up telephone numbers quickly. Each provider needs at least one exchange in each "rate center" in its territory. An "exchange" (or prefix) is the first 3 digits of your 7-digit local telephone number. Each exchange has 10,000 possible line numbers to assign. And there may be dozens of rate centers in the area code. The problem is that many of the newer service providers are small and have only a handful of subscribers in each rate center. Thus most of their assigned numbers are unused. Meanwhile, some carriers have reserved more exchanges than they will likely need, worsening the shortage.