Suffolk County's area code, 631, will welcome officially its new sibling -- 934 -- next year on July 16.

That's when the county's residential, business and wireless customers requesting new service, a new line or possibly to move their service could get the new code, according to the New York State Public Service Commission.

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At that point, carriers could still have a ready supply of 631 numbers, so the influx of the new code may 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.

storyState: 934 will be Suffolk's new area code

To help prepare customers to start dialing 10 digits instead of seven for intra-county calls with the addition of that second code, Suffolk residents as of Saturday are encouraged to begin dialing the 631 area code and seven digits, the commission said Thursday in a news release.

That test-run dialing phase ends next June 18, when 10-digit dialing will be required for all local calls, the commission said.

So that residents will be "good to go" at that point, Manning advises them to start reprogramming contact information in their phones to include the 631 code. Businesses can begin updating websites, stationery, anywhere their seven-digit numbers are advertised, he said.

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The second code came about because 631 was "running out of assignable telephone numbers," said a June 2014 report from the state Department of Public Service.