South Carolina's fourth area code will be 854, but no one is expected to get one of the new phone numbers until some time in 2015.

The 854 number will be South Carolina's first "overlay" area code, so it's expected to cause some confusion. It will become a second area code for the areas currently served by 843 so the 854 area code numbers will be assigned as the available 843 numbers run out.

So, at some point next-door neighbors might have different area codes, and everyone with an 843 or 854 area code will have to dial 10 digits to make a phone call.

The date when mandatory 10-digit dialing will begin has not been set, but based on current projections and regulatory approvals, it would likely be during the first half of 2015.

Nanette Edwards, chief counsel for the S.C. Office of Regulatory Staff, said the office learned of new area code number Monday from the administrators of the North American Numbering Plan.

The new number was actually set aside at least a decade ago but was not revealed - even to state regulators - until now, according to Thomas Foley, senior manager, data analysis, for Neustar.

"The reason we don't make these public is, periodically they change," Foley said.

Neustar is the company that serves as administrator for the North American Numbering Plan. Foley is one of three people in the nation who handles the planning of new area codes.

He said the 854 number was chosen from among the numbers available in South Carolina, which had to be numbers that weren't already used as a prefix within the current area code. In other words, no one in the 843 area code has a phone number that begins 843-854-XXXX.

Regulators don't want a situation where an area code is the same as the first three digits of local phone numbers.

"We have a finite number of numbers that we can use for area codes," Foley said.

The new number puts South Carolina in the unusual position of having all of the state's area codes begin with the same number, 8.

South Carolina's first area code was 803, back in the rotary telephone days. Cities with dense populations, such as New York (originally 212), got the best numbers that took the least time to dial, back when people had to literally dial a phone.

Reach David Slade at 937-5552