If you’ve ever wondered why your city has more than one area code—or why your carrier suddenly tells you to dial ten digits for a neighbor across the street—you’re living in an overlay. This guide breaks down what overlays are, how they differ from splits, and what they mean for residents, businesses, and anyone who buys phone numbers.
TL;DR
- Overlays add a new area code on top of the same geographic region instead of carving the map into new pieces.
- Everyone dials 10 digits for local calls where an overlay is in effect.
- Existing numbers don’t change. New numbers in the same neighborhood may simply carry a different area code.
- For businesses, plan ahead for printed materials, IVRs, CRM fields, and number inventory.
Quick background: NANP in one minute
The U.S., Canada, and several Caribbean countries share the North American Numbering Plan (NANP). Each standard number looks like this:
NPA-NXX-XXXX
Where:
- NPA = Numbering Plan Area = area code
- NXX = central office / exchange
- XXXX = line number
Phones, modems, faxes (RIP), and apps all draw from the same finite pool of NXX blocks inside each area code. When a region runs low on available numbers, regulators choose a relief method: split or overlay.
Overlay vs. split (and why overlays won)
Splits used to be common: a single area code was cleaved into two or more pieces, and some people had to change their numbers. That’s disruptive (think: business cards, signage, customers who can’t reach you).
Overlays avoid renumbering. A new area code is layered onto the same map, and new numbers are issued under the new code while old numbers keep their original code. The trade-off: 10-digit dialing becomes mandatory for local calls within the overlay.
Because overlays are less painful for consumers and businesses, most recent area-code relief plans choose overlays by default.
What 10-digit dialing really means
If your region has an overlay, you must dial:
- Area Code + 7-digit number for local calls
- 1 + Area Code + number for long-distance (or when your carrier requires the leading “1”)
Some devices need a nudge:
- Desk phones & PBXs: Update dial plans to allow 10-digit local calls.
- Fax lines & alarms: Confirm they dial 10 digits (or use a cellular/IP path).
- Speed dials, intercoms, call forwarding rules: Add area codes where missing.
Note: The nationwide designation of 988 for Suicide & Crisis Lifeline standardized 10-digit dialing in many area codes a while back. If you’re still dialing 7 digits, enjoy it while it lasts—most growing regions eventually move to 10.
Real-world overlay examples
These are simplified for clarity—city boundaries and “rate centers” don’t always match the lines you see on a street map.
How overlays change maps (and how to read ours)
On an overlay map, the same geography is labeled with multiple area codes. That’s not a mistake—it’s how overlays work. A few quirks to keep in mind:
- Rate centers vs. civic lines: Phone networks use rate centers, not city/county boundaries. That’s why your suburb might show an area code you rarely see—there’s probably a shared rate center.
- Boundary “fuzziness”: Mobile numbers are portable; people keep numbers when they move. A 305 could ring in Seattle. Maps show assignment, not where a phone physically is.
- Multiple NPAs per address: In a thick overlay, two tenants in the same building can have different area codes on the same day.
👉 Explore overlays on our interactive maps at AreaCodeMaps. Zoom to your street and toggle labels to see how NPAs stack in your neighborhood.
What residents should do (a simple checklist)
- Save local contacts with the area code. “555-0123” should become “(###) 555-0123.”
- Update smart-home and safety devices. Doorbells, alarm panels, and medical alerts often have stored numbers.
- Mind caller ID filters. If you whitelist “local numbers,” expand the filter to include all overlay codes in your area.
- Watch scams, not area codes. Overlays don’t cause spam—but spoofers can look “local.” Treat unknown calls with caution.
What businesses should do (don’t wait)
Inventory everywhere a phone number lives
- Website headers & footers
- Google Business Profile, Yelp, Apple Business Connect
- Social bios, email signatures
- In-store signage, vehicle wraps, uniforms
- Printed collateral (menus, brochures, coupons)
- IVR prompts, voicemail greetings, call flows
- CRM and marketing automation templates
Normalize numbers to E.164 internally
Store numbers like +1NXXNXXXXXX. It prevents formatting bugs when you pass leads between systems or text-enable a line.
Update PBX/SIP dial plans
- Ensure 10-digit local dialing is accepted.
- Keep emergency and N11 codes (e.g., 911, 811) unblocked.
- If you use extension dialing, avoid conflicts with local prefixes.
Plan number inventory in advance
- If you care about a specific NPA (e.g., “We want a 212”), order early—vanity and legacy-code inventory goes fast when an overlay is announced.
- Consider DIDs for each overlay code if you route by caller “locality” in ads.
Common myths to ignore
- “New code = long-distance.” Not true. Billing depends on your plan and carrier, not the overlay code itself.
- “I’ll be forced to change my number.” Overlays are designed to avoid renumbering.
- “Area code proves where someone is.” Thanks to porting and mobile, it doesn’t.
Glossary (fast definitions)
- Overlay: A new area code assigned to the same geographic area as existing codes.
- Split: Dividing a region into new geographic areas, each with a different code; renumbers some customers.
- Rate Center: A telecom-defined location used for routing and rating calls.
- NXX Block: A group of 10,000 numbers (sometimes allocated in smaller “pooled” chunks).
- N11 Codes: Three-digit service codes like 211, 311, 411, 511, 611, 711, 811, 911.
FAQs
Do I need to reprint everything with a new area code?
No. Your number doesn’t change when an overlay arrives. Reprint only if you choose to adopt a new number.
Why did my neighbor get a different area code than me?
Carriers issue from what’s available. In overlays, multiple NPAs serve the same addresses.
Will 7-digit dialing come back?
Unlikely in growing markets. Overlays and nationwide 988 compliance mean 10-digit dialing is the norm.
Have a tip about a newly announced overlay or a correction for your local map tile? Drop us a note—we’re always improving our data.