Area Code 310
California
Area code 310 serves California, primarily Los Angeles, in the Pacific Time (PT) time zone. It has served the region since 02-Nov-1991.
Overlay Area Code
This area code is part of an overlay region, meaning the same geographic area is served by multiple area codes. Overlay codes were introduced to meet growing demand for phone numbers without requiring existing customers to change their numbers.
This area code shares its geographic region with: area code 424 (Los Angeles).
In service since: 02-Nov-1991
Area Code Splits
Parts of this area code’s original geographic region were later assigned new area codes through splits. When a split occurs, some customers in the original area code region are assigned the new area code.
Split into: area code 562 (Long Beach).
Historical Timeline of Area Code 310
Area code 310 has one of the most eventful histories of any North American numbering plan area, marked by a geographic split, a controversial overlay fight, and a seven-year regulatory saga. The story begins with the original 213 area code, established in 1947 as one of the first three California area codes serving the entire Los Angeles region. Source: Wikipedia — Area codes 310 and 424
- November 2, 1991: Area code 310 is created from a geographic split of area code 213 to relieve number exhaustion in the Los Angeles region. The new 310 NPA covers the Westside, South Bay, and Harbor areas of Los Angeles County, including Beverly Hills, Santa Monica, Malibu, Torrance, and Long Beach. Source: CPUC D.03-10-060
- January 25, 1997: Area code 562 is split from 310, taking the southeastern portion of Los Angeles County (Long Beach, Gateway Cities) and parts of Orange County. The split was originally intended as an overlay for cellular and pager services, but the CPUC chose a geographic split instead. Source: Wikipedia — Area code 562
- May 7, 1998: The CPUC issues Decision D.98-05-021, approving area code 424 as an all-services overlay for 310 — the first area code overlay ever approved in California. The decision required mandatory 1+10-digit dialing for all local calls. Source: CPUC Comment Decision — 310 Relief Background
- September 9, 1999: The California State Assembly passes the Consumer Area Code Relief Act of 1999, pressuring the CPUC to halt the overlay. One week later, on September 16, 1999, the CPUC adopts Decision D.99-09-067, suspending the 424 overlay and instituting number conservation measures including number pooling and fill rate requirements. Source: CPUC Comment Decision — 310 Relief Background
- March 16, 2000: The CPUC Telecommunications Division releases a report finding at least 3 million unused telephone numbers in the 310 area code, revealing that perceived exhaustion was largely a distribution problem. Of 2.7 million unused numbers held by carriers, 470,000 were in blocks with less than 10% contamination. Source: CPUC Report on the 310 Area Code (March 2000)
- September 29, 2000: The CPUC adopts Decision D.00-09-073, approving a geographic split (Alternative 1A) as a backup contingency plan. NANPA projected the split 310 NPA would have a life of only 3.2 years, making it an inefficient relief option. Source: CPUC D.00-09-073 — Geographic Split Backup Plan
- August 25, 2005: The CPUC unanimously approves the all-services overlay for 310 in Decision D.05-08-040, replacing the geographic split backup plan. PUC President Michael R. Peevey stated: "The overlay approved today is the first time this form of area code relief has been used in California." Source: CPUC Press Release — PUC Approves All-Services Overlay for 310
- July 26, 2006: Mandatory 1+10-digit dialing begins for all calls within the 310/424 area. New 424 numbers begin to be assigned on August 26, 2006, completing the first overlay implementation in California history. Source: CPUC D.05-08-040 — All-Services Overlay Approval
Unique Facts About Area Code 310
Area code 310 holds several unique distinctions within the North American Numbering Plan, from a landmark unused-numbers discovery to a seven-year regulatory delay that reshaped California telecommunications policy. Source: Wikipedia — Area codes 310 and 424
- 3 Million Unused Numbers Discovered — A CPUC Telecommunications Division study in March 2000 found at least 3 million unused telephone numbers in the 310 area code. Of the 2.7 million unused numbers held by carriers, 470,000 were in blocks with less than 10% contamination — nearly pristine blocks being hoarded by carriers. The root cause was the traditional 10,000-block allocation system, a holdover from the monopoly era when only one carrier served each territory. With over 200 carriers operating in California, the old system created massive waste. Source: CPUC Report on the 310 Area Code (March 2000)
- Seven-Year Regulatory Delay — The 310 overlay experienced one of the longest regulatory delays in California area code history. The CPUC first approved the 424 overlay on May 7, 1998 (Decision D.98-05-021), but suspended it on September 16, 1999 (Decision D.99-09-067) after a firestorm of negative public reaction and the passage of the Consumer Area Code Relief Act of 1999. The overlay was not re-approved until August 25, 2005, and finally implemented on July 26, 2006 — nearly seven years after the original approval. Source: CPUC Comment Decision — 310 Relief Background
- 3.2-Year Split Life Expectancy — NANPA projected that if the geographic split (Alternative 1A) had been implemented for the 310 area code, the resulting 310 NPA would have had a life of only 3.2 years before requiring further relief. This extremely short life expectancy was a key factor in the CPUC's decision to pursue an overlay instead of a split, since splitting 310 would simply redistribute the same number resources without addressing the underlying allocation inefficiency. Source: CPUC D.00-09-073 — Geographic Split Backup Plan
- FCC Contamination Threshold Waiver — The FCC granted a unique contamination threshold waiver for the 310 and 909 area codes in August 2003, raising the allowable contamination rate from 10% to 25%. The FCC estimated this would extend the life of the 310 area code by approximately one additional month. Since the waiver took effect, carriers returned 413 additional blocks to the 310 number pool. Source: CPUC D.03-10-060 — 310 Area Code Conservation Review
- Number Pooling Saved 120 Prefixes — The number pooling trial in the 310 area code, ordered by the CPUC in December 1999 and implemented for wireline carriers on March 18, 2000, saved an estimated 120 prefixes by allowing numbers to be allocated in blocks of 1,000 instead of 10,000. Wireless carrier pooling began later on November 24, 2002. The 310 trial was among the first in California and served as a proof of concept for the statewide program. Source: CPUC D.03-10-060 — 310 Area Code Conservation Review
- Affluent Service Area — The 310/424 overlay complex serves one of the most affluent regions in the United States, with a combined population of approximately 1,891,078. The service area includes Beverly Hills, Malibu, Santa Monica, and Manhattan Beach, with a median household income of $87,760 — significantly above the national median. The area is home to major entertainment and technology industry headquarters, and 35.5% of residents hold a bachelor's degree or higher. Source: Wikipedia — Area codes 310 and 424
FCC Regulatory History
The regulatory history of area code 310 reflects California's evolution from aggressive area code splits to conservation-first policies. Source: CPUC Comment Decision — 310 Relief Background
| Year | Event | Docket | Regulatory Action & Impact |
|---|---|---|---|
| 1998 | First overlay approved in California | D.98-05-021 | CPUC approves area code 424 as an all-services overlay for 310 — the first overlay in California. Required mandatory 1+10-digit dialing, generating immediate public opposition. Source: CPUC Comment Decision |
| 1999 | Overlay suspended; conservation measures adopted | D.99-09-067 | After the Consumer Area Code Relief Act of 1999 (September 9), the CPUC suspends the overlay on September 16, 1999, instituting number pooling, fill rate requirements, and sequential numbering rules. Source: CPUC Comment Decision |
| 2000 | Backup geographic split adopted | D.00-09-073 | CPUC adopts a geographic split (Alternative 1A) as a backup plan. Split would divide 310 along Imperial Highway. NANPA projected the split 310 NPA would have a life of only 3.2 years. Source: CPUC D.00-09-073 |
| 2003 | FCC contamination threshold waiver | D.03-10-060 | FCC raises contamination threshold from 10% to 25% for 310 and 909, extending 310's life by one month. Carriers return 413 additional blocks to the number pool. CPUC adopts 75% fill rate requirement. Source: CPUC D.03-10-060 |
| 2005 | All-services overlay approved (final) | D.05-08-040 | CPUC unanimously approves the 424 overlay, replacing the geographic split plan. PUC President Peevey: "The first time this form of relief has been used in California." Mandatory 10-digit dialing begins July 26, 2006. Source: CPUC D.05-08-040 |
| 2006 | Overlay implemented | NANPA PL | Mandatory 1+10-digit dialing takes effect July 26, 2006. New 424 numbers assigned from August 26, 2006. The 310/424 overlay becomes the first in California. Source: CPUC Press Release |
County Coverage
Population-weighted county share based on aggregated ZCTA population (100% = total mapped population for area code 310).
| County | Population | Share |
|---|---|---|
| Los Angeles, CA | 1,875,164 | 99.2% |
| Ventura, CA | 15,914 | 0.8% |
Call Context
This area code includes Los Angeles and West Los Angeles and the South Bay in California. The region extends well beyond the urban core into surrounding suburbs and communities.
Nearby Area Codes
Area codes geographically closest to 310.
Other Area Codes in California
Area codes that also serve California, linked for easy comparison.
Frequently Asked Questions
Common questions about area code 310 and how phone numbering works.
Phone numbers are assigned based on where the number was originally provisioned, not the caller's current location. Mobile phones retain their number when users move, and businesses may use numbers from regions where they don't have a physical presence. VoIP services can also provision numbers from virtually any area code.
Yes, mobile phones can have numbers from any area code in the region they were activated. Wireless carriers assign numbers from available pools regardless of phone type. When users change carriers or move to new areas, they typically keep their original number, which may have a different area code than their current location.
Start by looking up the area code on this site to understand its general geographic region. For the specific number, options include using your carrier's caller ID features or checking public directories. If you suspect fraud, you can report it to the FTC. To file a complaint about robocalls or spoofed numbers, visit the FCC Consumer Complaint Center. You can also register your number with the National Do Not Call Registry to reduce unwanted calls. Keep in mind that caller ID can display any name the caller chooses to set.
When an area's pool of available phone numbers runs low, regulators may introduce an "overlay" area code that covers the same geographic territory as the original. Both codes coexist, and new numbers are assigned from whichever code has availability. This area code shares its region with area code 424. Learn more in our overlay vs split guide.
While Los Angeles is a prominent city in this area code's coverage, the code serves the broader surrounding region as well. Area codes are assigned geographically and typically cover multiple cities, towns, and communities beyond any single anchor city.
This area code covers a metropolitan region with high population density. Dense urban areas typically have higher call volumes and may have multiple overlapping area codes to meet demand for phone numbers. Businesses and residents in these areas are more likely to need additional numbering resources.