In a few weeks, dialing seven digits won't get you anywhere in much of central Ohio.

In a few weeks, dialing seven digits won't get you anywhere in much of central Ohio.

Beginning March 21, residents who live and work in the region served by the 740 area code will need to dial 10 digits to make a local phone call. About a month later, the 220 area code could make its debut in the region.

The 740 area code covers most of Delaware County, as well as southeastern Ohio and the majority of other counties bordering Franklin County.

Katie Salvator, spokeswoman for the Public Utilities Commission of Ohio, said anyone who fails to dial 10 digits after March 21 will be greeted by a recording that reminds callers about the new rules.

Along with remembering to dial an area code before making local calls, Salvator said residents should check to make sure cellphones, security systems and "anything that automatically dials" have the proper area codes saved internally.

Numbers with the 220 area code will not be assigned to customers until, at earliest, April 22. Salvator said the PUCO has no way of determining the exact date when the supply of 740 numbers will be exhausted.

After the change, any calls within the 220 or 740 area codes still will be considered local, and residents still will be able to dial 911 by using only three numbers.

PUCO officials have said the need for the new area code largely has been driven by machines such as credit-card readers and security systems that require phone numbers.

When the need for the new area code became apparent, the PUCO faced one of two choices: Split off a portion of the region served by the 740 area code and give it a new code; or begin assigning numbers with a new area code throughout the region.

After receiving public comment largely against a split, the PUCO decided on the "overlay" option.

"Nobody's going to lose their (current) phone number, which is good," Salvator said.

Central Ohio likely will see a second overlay implemented next year. Salvator said the PUCO expects the supply of numbers with the 614 area code to be exhausted by the second quarter of 2016.

Residents of Columbus and its closest suburbs could be assigned numbers with a 380 area code next year.