909 Area Code Map and Boundary Guide: Cities, Counties, and 840 Coverage

Understand the full story behind 909 Area Code Map and Boundary Guide: Cities, Counties, and 840 Coverage with expert analysis.

Does the introduction of the 840 area code change my existing 909 phone number?
No. The rollout of the 840 area code is a pure overlay, meaning existing telephone assignments remain unchanged. Only new lines, secondary cell accounts, or newly provisioned business trunks receive the 840 area code assignment.

Which cities in Los Angeles County fall under the 909 area code?
The primary Los Angeles County municipality within 909 is Pomona, alongside neighboring eastern communities including Claremont, San Dimas, and La Verne. Sections of Diamond Bar and Walnut also share 909 exchanges where carrier wire-center boundaries overlap county lines.

Are calls made from a 909 number to an 840 number billed as long-distance?
No. Geographic calling ranges and local tariff zones are preserved across the overlay network. If a call from your home or business was considered a local call under 909, it remains a local call when dialed to an 840 number.

Do medical alert systems and security alarms work under ten-digit dialing?
All automated dialing devices, including home security alarms, commercial fire panels, and personal medical alert monitors, must be programmed to dial the complete ten-digit phone number. Systems left configured with seven-digit dialing strings fail to complete connections across the 909/840 overlay grid.