If you live in the more populated segments of New Jersey, you may be surprised to learn that many residents still have the option to dial just seven digits in order to reach someone on the phone.

For a big chunk of New Jersey, that's about to change.

A new 640 area code — the 10th in the state — is being added to the same region that's currently served by area code 609. The geographic area spreads from Mercer County down the southeast portion of New Jersey to Cape May.

Beginning Aug. 18, anyone with a 609 area code can no longer dial just seven digits for local calls. Calls within the same area code will require 10-digit dialing, and calls to any other area code will require a '1' before the area code and seven-digit number.

NJ Board of Public Utilities

"If they're calling their next door neighbor, they would just have to dial the area code," explained Joseph Fiordaliso, president of the New Jersey Board of Public Utilities.

Fiordaliso said the change is needed to ensure a continuous supply of phone numbers.

"As the most densely populated state in the union, that density is expanding and requires more phone numbers," he said.

The 640 area code will be assigned to new telephone lines or services as early as September 18. Those with a 640 area code will have to follow the same rules as 609 customers.

Beginning Saturday, one's call will not be competed without the new dialing procedure, the BPU states. A recording will tell callers to hang up and try again.

The addition also affects those within the 856 area code (southwest New Jersey). While these customers can still just dial seven digits within their own area code, all other calls will require at least 11 digits.

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Contact reporter Dino Flammia at dino.flammia@townsquaremedia.com.