Will the U.S. Ever Run Out of Telephone Numbers?

Prior to the 1960s, the telephone system used something called the 2L-5N — or two letters, five numbers — format. The letters would be the first two letters of a word, typically the name of a neighborhood, and the numbers corresponded to the individual you were calling. An oft-cited example is Lucy and Ricky Ricardo's phone on the TV show "I Love Lucy." Their phone number was MU 5-9975, for their Murray Hill neighborhood.

To dial a phone number in those days, you'd pick up the phone and speak to a real human operator, who'd physically plug you into the telephone network you were trying to reach. It was easy enough to do for local calls, but long distance got a bit complicated, and as the phone network grew, it called for a new system. A seven-digit system called "all number calling" ditched the letters. Instead, the first three digits corresponded to a telephone provider, while the last four identified the phone-owner. Soon, even that wasn't enough.

Enter the area code. In 1951, the North American Numbering Plan Administrator (NANPA) — governors of the U.S. phone number system — added the first three-digit area code, New Jersey's, which was 201. At first, there were 86 area codes. Currently there are 335 total area codes, but the phone numbers associated with them are going fast.

"There are area codes that become exhausted," says Kylie Dick, a sales manager for phone number management company NumberBarn. "There's only a certain number of them within each, and once they're gone, they're gone."

That's not to say numbers don't sometimes reenter circulation. "We get a lot of customers asking if we have a 'fresh, clean, unused number,'" says Dick. "At this point, most numbers are 'recycled,' so at one point in their history they were probably used by someone and then [the numbers] went back to the carrier."

But when an area code is close to being "exhausted," meaning all its numbers have been assigned, NANPA introduces a new area code for that region. But area codes, too, are finite. There are 800 possible three-digit combinations (using 0 or 1 as the first digit of an area code is invalid), but many are unusable (think 911) or reserved for official use. Ultimately, the math works out to a bit more than 5 billion total available phone numbers. In North America, well over half of those are already assigned.

Some plans have been proposed to add more digits. A report created by the Alliance For Telecommunications Industry Solutions explained that adding one digit to the area code and one to the dialing prefix would create an additional 640 billion possible numbers. But it would be much easier said than done: Everything formatted for a 10-digit number would have to be altered to work with two extra digits.

Others believe that by the time 10-digit numbers near total exhaustion, the world will have transitioned away from telephony and toward internet-based calling. In that future, it's difficult to believe 10-digit numbers would be anything but obsolete. "One way or another, your phone number will eventually become a coding afterthought," wrote Drew Magary for Vice.

We're certainly not there yet though, says Dick. Phone numbers remain a hot commodity, and the shortage of certain desirable numbers or area codes only serves to increase demand.

"There are certain patterns of numbers that people are trying to purchase," she says. "They're wanting a number that is highly memorable. It just makes for easier marketing."