"E" is Eastern Time Zone, "C" is Central Time Zone, "M" is Mountain Time Zone, and "P" is Pacific Time Zone. Occasionally, an area code will fall in more than one time zone. In this case, the abbreviation is a combination of the previous abbreviations. Some area codes are shown with time zones referencing Universal Coordinated Time (UTC).
Additional technical status can be retrived from the North American Numbering Plan Administration on the 657 area code specific link here.
ROYAL STREET COMMUNICATIONS, LLC, ALLEGIANCE TELECOM, INC. - CA, PACIFIC BELL, NEW CINGULAR WIRELESS PCS, LLC, TELCENTRIS COMMUNICATIONS, LLC - CA, CELLCO PARTNERSHIP DBA VERIZON WIRELESS - CA, COX CALIFORNIA TELCOM, INC. - CA