Prefix 909-378 — Diamond Bar, CA

NANPA CO code assignment, current as of July 28, 2026.

Area code
909
Prefix (NXX)
378
Rate center
Diamond Bar
State
California
Time zone
Pacific
Code holder
MCIMETRO ACCESS TRANSMISSION SERVICES LLC - CA
OCN
7240
Pooled
Yes (thousands-block pooling)
Assigned
2013-07-31
LATA
730

Numbers in the 909-378 prefix are registered to the Diamond Bar rate center in CA, inside area code 909. The prefix is the second block of a ten-digit US number (909-378-XXXX) and pins the number to a billing locality.

Code-holder of record: MCIMETRO ACCESS TRANSMISSION SERVICES LLC - CA (OCN 7240), assigned July 31, 2013. The prefix is pooled: its ten thousands-blocks can be shared among several carriers, so different 909-378 numbers may be served by different companies.

The rate center lies in the Los Angeles-Long Beach-Anaheim, CA Metropolitan Statistical Area. The serving LATA is 730. Local time follows the Pacific zone.

Spoofing means this prefix on your screen doesn't guarantee a Diamond Bar caller. Verify independently before trusting a request for money or data.

Neighboring prefixes

Prefixes adjacent to 909-378
PrefixRate centerCode holder
909-375 Big Bear City BANDWIDTH.COM CLEC, LLC - CA
909-376 Ontario T-MOBILE USA, INC.
909-377 Upland NEW CINGULAR WIRELESS PCS, LLC
909-379 San Bernardino LEVEL 3 TELECOM OF CALIFORNIA, LP - CA
909-380 San Bernardino FRONTIER CALIFORNIA INC.
909-381 San Bernardino FRONTIER CALIFORNIA INC.

FAQ

Where is 909-378 located?

The prefix is assigned to the Diamond Bar rate center in CA, area code 909. It is part of the Los Angeles-Long Beach-Anaheim, CA Metropolitan Statistical Area.

Which company owns 909-378 numbers?

MCIMETRO ACCESS TRANSMISSION SERVICES LLC - CA holds the code, but the prefix is pooled — individual thousands-blocks can be assigned to other carriers, and numbers may be ported to any provider.

Is a call from 909-378 safe to answer?

The prefix itself says nothing about the caller. Legitimate Diamond Bar businesses and spoofed robocalls can both display it. Never share personal data with an unverified inbound caller.