PORTLAND — With 16 counties, two congressional districts, vast uninhabited tracts between its mountainous west and coastal peninsulas, Maine has just one area code: 207.

It’s a flag we all fly. But that may not be forever.

The projection for when there won’t be room enough for all of us in that beloved area code is the first quarter of 2019. That projection has steadily moved further into the future in recent estimates, which are made twice a year.

John Manning, a senior director at Neustar, where he oversees the North American Numbering Plan Administration, said 207 isn’t hitting its cap in the immediate future, but it’s not too early to start planning for that eventuality.

“It’s a matter of when for all of them, but some of them based upon the demand … it may be a significantly long period of time,” Manning said, noting the area code of Guam has a pretty long horizon for exhaustion. “In the case of 207, we saw a lot of activity and thought we were going to have to do relief, but we implemented these optimization measures and significantly slowed it down.”

The major trend bringing the area code closer to exhaustion is a multiplication of devices with phone numbers. A family of four, for example, might only have had one phone line before cellphones.

Now, each family member could have a number. And there’s a proliferation of connected devices with their own separate numbers.

Rich Kania, a senior telecommunications analyst at the Maine Public Utilities Commission, said hospitals offer a prime example.

“Hospitals use a lot of numbers because they use them for every device and every room,” Kania said. “Even though we have fewer wireline customers, we have more wireline numbers in use today.”

The trends pushing back that exhaustion date are Maine’s slow or stagnant population growth and number conservation strategies of the state utilities commission and Neustar.

The exhaustion estimates depend on current and projected demand for new three-digit prefixes (called collectively the numbering plan area, NPA, or central office code) that are the first part of a seven-digit area code. Those prefixes contain about 10,000 possible phone numbers.

With 102 Maine prefixes unassigned as of this week, according to Neustar data, that works out to about 1.02 million possible numbers still available in the 207 area code, compared to about 6.71 million that are already assigned.

But many of those individual phone numbers will go unassigned. That’s because prefixes are assigned to a company in a certain rate center, or geographic boundary set up for billing purposes.

Those numbers will get divvied out into blocks of 1,000 by Neustar to a local exchange carrier, but not all of those 1,000 possible numbers will get assigned. And those unassigned numbers don’t go back into the pot of available numbers.

Manning said slow growth in the number of assigned prefixes led Neustar to back out its projection of when Maine would need a second area code. Those estimates are based on historical demand but also projections of demand from existing exchange carriers.

Hopeful projections after Maine deregulated its telephone industry at the end of 2012 were a likely factor in the projection of that year, which expected 207 would be exhausted by the third quarter of 2016.

And that projection dictates when the state has to start planning. When the area code is projected to exhaust in three years, Neustar will begin planning with the telecommunications industry, devising a plan for how to introduce a new area code and presenting that to the Public Utilities Commission.

Kania said that process would involve one major decision: whether to split the state into two area codes or overlay the new area code throughout the entire state.

After that, he said, new central office codes would get assigned from that area code and mandatory 10-digit dialing could be soon after.

But strategies for conserving numbers could continue to hold back that dreadful day. In order to get assigned a block of 1,000 numbers, a certified local exchange carrier, or CLEC, need only ask.

That raised concern with deregulation in 2012, according to Andy Hagler, director of the PUC’s telecommunications division. Hagler said there were many new telecom competitors coming onto the scene after deregulation, all seeking blocks of telephone numbers.

“It was a very exciting time when they thought they would be able to make a good business selling local exchange service,” Hagler said. “We were very careful in requiring that those companies show us that within six months of providing service that they would actually provide service.”

Otherwise, the blocks of numbers are put back into the pool of available numbers.

Though number conservation measures have fended off Maine’s division under two area codes, Manning said that, eventually, that day will come.