Worried that the growth of telephone numbers means an iconic symbol of New Hampshire might be elbowed aside in a few years, Gov. Chris Sununu is telling the state to “investigate durable strategies … for lengthening the useful life of the 603 Area Code.”

His executive order, issued Tuesday, is the latest in a long line of state actions designed to keep New Hampshire as a state where everybody has the same area code, one unique to us since area codes were created in 1947. In 1999, for example, the Legislature passed a law telling the Public Utilities Commission to “adopt telephone number conservation measures to the maximum extent allowed by federal law for area code 603.”

Because phone numbers are controlled by the Federal Communications Commission, however, there isn’t a whole lot that states can do.

Sununu’s latest order tells the Department of Energy to study ways to extend the life of 603 as our only area code but also acknowledges that a second code might become necessary. The order points out that a study by the North American Numbering Plan, which oversees area codes in most of the continent, estimated that 603 could run out of phone numbers as early as 2027.

The order tells the Department of Business and Economic Affairs to undertake “a study of business practices related to number usage, and business costs and opportunities that may result from the implementation of a second area code.”

New Hampshire has been working to keep 603 since at least 1990, when reports first surfaced that so many phone numbers were being used that we might have to get a second area code.

In theory, an area code can include 7.7 million different seven-digit phone numbers after discounting those that aren’t allowed such as exchanges starting with a zero. That’s far more than needed, but the problem is that phone numbers are allocated in a very inefficient manner because of how the telephone switching network was constructed in the pre-digital era.

Overcoming those inefficiencies explains why New Hampshire has been told several times that 603 was getting full, only to be told later on that there was room for more numbers after all.

The North American Numbering Plan started in 1947 to standardize phone systems and allow inter-connection while keeping phone numbers unique. The system now covers Canada and parts of the Caribbean, but not Mexico. Its rules determine how carriers dole out phone numbers in geographic areas covered by phone exchanges, which are the first three digits of a seven-digit phone number.

The original switched-network design of the telephone system meant that each exchange carried 10,000 potential phone numbers, corresponding to the final four digits of the phone number, from 0000 to 9999. If there aren’t enough customers in the service area of the exchange to need all those numbers, many will sit unused. A 2019 petition from New Hampshire to the FCC pointed out that the town of Derry was given “enough numbers to provide every resident with seven or more unique, geographically relevant phone numbers.”

New Hampshire is one of several states that has asked the Federal Communications Commission to allow far more efficient assigning of phone numbers, which would extend the life of area codes much more.

This discussion comes even as the whole idea of area codes becomes less and less relevant, because cell phones and voice-over-Internet have frayed the historic and technical link between phone numbers and geographic location.