For the next 13 years, at least, you’ll know when a call comes in from another Montana number.

The Montana Public Service Commission this week said efforts to allocate phone numbers more efficiently will preserve the state’s beloved 406 area code until 2031.

After that date, the number will likely tap out under the state’s current rate of growth.

“The 406 area code is a unique part of our heritage in Montana,” said PSC commissioner Bob Lake of Hamilton. “It’s become such an integral part of our state’s identity that some businesses have built their entire brand around the novelty of our single area code.”

Montana is one of 12 remaining states with a single area code. The number has been adopted in everything from T-shirt logos to web domains.

PSC spokesman Chris Puyear said Montana’s 406 area code was expected to exhaust by 2019. That estimate, made just four years ago, was extended under efforts by the PSC and Montana telecommunication companies to make more efficient use of phone numbers.

Puyear said the FCC informed the state on Monday that the single area code had a few more years.

“Population increases plus the explosion of cellphone subscriptions combined with correlating phone number growth will eventually force the state of Montana to adopt an additional three-digit area code,” Puyear said. “There are currently 1 million cellphone subscribers in Montana compared to 400,000 landline customers.”

Lake said a PSC order rendered in 2013 extended the life of the 406 area code. That order implemented a policy known as “mandatory number pooling,” which required existing phone carriers to make available numbers they are not using.

The order also limited the amount of additional telephone numbers that can be assigned to new providers, or providers requesting additional numbers.

“Basically, it ensures that carriers are not sitting on a bunch of unused numbers, which could hasten the area code exhaustion date,” Lake said.

The FCC requires planning for a new area code to begin three years in advance of the forecast area code exhaustion date.