An area code reaches "exhaust" when nearly all of the telephone prefixes within that area code are assigned. Prefixes follow the area code and are the first three numbers of a customer's local phone number. Faxes, pages, cell phone calls, ATMs and pay-at-the-pump gas stations are just some of the ways phone numbers are being used.
The North American Numbering Plan Administrator has notified the Public Utilities Commission of Ohio (PUCO) of the following exhaust dates* for Ohio area codes:
| Area Code | New Exhaust Year | New Exhaust Quarter | Old Exhaust Year | Old Exhaust Quarter |
| 216 | 2025 | 2Q | 2024 | 4Q |
| 330/234 | 2028 | 4Q | 2028 | 3Q |
| 419/567 | 2021 | 2Q | 2020 | 3Q |
| 440 | 2017 | 3Q | 2016 | 3Q |
| 513 | 2015 | 4Q | 2015 | 1Q |
| 614 | 2016 | 1Q | 2015 | 4Q |
| 740 | 2010 | 4Q | 2010 | 2Q |
| 937 | 2011 | 3Q | 2011 | 3Q |
*as of 2007
Relief for area code exhaust is usually done by either dividing the area code with a geographic split or by adding an additional area code to the existing one, commonly called an overlay. The PUCO has decided that an overlay will be used in the 330, 419, 513, and 614 area codes.
As the name suggests, the new area code "overlays" the pre-existing area serving the identical geographic area. The benefit of an overlay is that customers retain their existing area codes. Only new lines get the new area code. An overlay requires all customers, including those with telephone numbers in the pre-existing area code, to dial area codes in addition to the seven-digit number for local calls (10-digit dialing).
330/234 - Mandatory 10-digit local dialing in 330/234 began on October 1, 2000.
419/567 - Mandatory 10-digit local dialing began in 419/567 on December 1, 2001.
New and current subscribers will have a high likelihood that they will be able to obtain at least some telephone numbers in the 330 and 419 area codes for some time to come. This is due to the volume of currently unused telephone numbers in the 330 and 419 area codes and due to the recycling of telephone numbers as customers terminate use of existing lines.
513/283 - Permissive 10-digit local dialing began in 513/283 on January 15, 2001. The implementation of mandatory 10-digit local dialing and the assignment of numbers in the 283 area code has been suspended due to a decrease in number assignment. Permissive 10-digit local dialing will continue until the Commission sets a new mandatory 10-digit dialing date. Subscribers must continue to ensure that upgrades and changes are made to their telecommunications systems or equipment, including alarm systems, to allow for permissive 10-digit local dialing.
614/380 - Permissive 10-digit local dialing began in 614/380 on August 18, 2001. The implementation of mandatory 10-digit local dialing and the assignment of numbers in the 380 area code, like that in the 513/283 area code, has been suspended due to a decrease in number assignment. Permissive 10-digit local dialing will continue until the Commission sets a new mandatory 10-digit dialing date. Subscribers must continue to ensure that upgrades and changes are made to their telecommunications systems or equipment, including alarm systems, to allow for permissive 10-digit local dialing.
The overlay plans treat all existing 330, 419, 513, and 614 customers equally by allowing them to retain the 330, 419, 513, and 614 area code on all existing lines and, as necessary, to have the new area code assigned to new telephone lines in the future. Also businesses will benefit by not having to incur the additional expense of changing advertising materials.
The requirement for all existing 330, 419, 513, and 614 area code customers to change their local dialing patterns is the most significant impact of the overlay plan.