Area code 909 is an important part of the telephone numbering plan in the United States, specifically in Southern California.

Geographical Coverage: Area code 909 serves a portion of the Inland Empire in Southern California. This includes parts of San Bernardino County, Riverside County, and a small portion of Los Angeles County. Major cities within this area code include San Bernardino, Riverside, Ontario, and Rancho Cucamonga.

Establishment and History: The 909 area code was created in 1992 as a split from the 714 area code. This division was necessary to accommodate the growing demand for telephone numbers in the region, a common issue in rapidly developing urban areas.

Recent Changes and Overlay Area Code: In 2004, the western portion of the old 909 area was split off into a new area code, 951. Additionally, to address the continued demand for numbers, an overlay area code, 840, was introduced to the 909 region in 2021. With this overlay, 10-digit dialing (area code + phone number) became mandatory for all calls within the 909 region.

In conclusion, area code 909 is more than just a telecommunication identifier; it represents a densely populated and economically vibrant region of Southern California. Its evolution, including the addition of an overlay code, reflects the dynamic growth and technological advancement in this area.