Officials are urging Indiana residents in the 317 area code to begin dialing 10 digits for all local calls.
The change is meant to help customers transition to the addition of the 930 area code in southern Indiana.
The Indianapolis area code is expected to run out of telephone numbers by 2017.
Medical and law enforcement officials have raised concerns about the transition 10-digit dialing in southern Indiana.
Residents living within the current 812 area code region will have to dial using 10 digits starting Sept. 6.
The additional area code will be added using an "overlay" method which will require everyone in the 812 area to start dialing 10 digit phone numbers.
The recommendation means new phone numbers would have a different area code, while existing numbers would keep the 812 code.
Residents say they would rather have two different area codes in the same region, than force some Hoosiers to get new phone numbers.
The 812 area code for Southern Indiana is set to run out of numbers by 2015.