The state Public Service Commission is urging residents and businesses in Suffolk County to prepare for life with the new 934 area code and the start of 10-digit dialing.

Residential, business and wireless customers within Suffolk’s existing 631 area code will be subject to 10-digit dialing — 631 or 934 plus the seven-digit local number — starting June 18, the commission said Monday in a reminder to Long Islanders.

That means that to be good to go, now is the time to reprogram the local seven-digit numbers stored in personal phones, as well as be sure that any service that involves automatic dialing, such as an alarm system, has been updated with the code.

There will be no need to dial a “1” for calls made from a Suffolk number to another Suffolk number, as it remains a local call, officials said.

Phone customers since last July have had the opportunity to get into the swing of 10-digit dialing, with Suffolk residents being in what the PSC calls a “permissive dialing phase.”

That permissive option goes away, though, as of 12:01 a.m. on June 18, when intra-county callers who slip and dial just seven digits will hear a recording telling them to hang up and dial again, using the area code, a PSC spokesman said.

For now, the only code in town remains 631, but after 934 makes its debut on July 16, it will gradually be added into the mix. Existing phone numbers are to remain the same, but anyone in the county requesting new service, an added line or possibly a move of their service, could be assigned the new code.

That goes for residential, business and wireless service.

As of that date, carriers could still have a ready supply of 631 numbers, so the influx of the new code could take time to build up steam, said John Manning, senior director of the North American Numbering Plan Administration, which oversees telephone resources, including area codes.

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This second code is coming about because 631, which was created for Suffolk in 1999 as the result of a split from the Island’s 516 area code, “is running out of assignable telephone numbers, and implementation of a new area code is necessary,” said a June 16, 2014, report from the state Department of Public Service.

The “overlay” approach that lets current customers keep 631 while new customers may be assigned 934, was approved in December 2014 over a “geographic split,” which would have seen residents on one side of a line keeping 631 and those on the other making the switch. The PSC determined the overlay was “easier to implement from a technical standpoint and less expensive from a customer standpoint, especially for business customers,” officials said in the news release at the time.

With Gary Dymski