California Code, Code of Civil Procedure - CCP § 213

Unless excused by reason of undue hardship, all or any portion of the summoned prospective jurors shall be available on one-hour notice by telephone to appear for service, when the jury commissioner determines that it will efficiently serve the operational requirements of the court.

Jurors available on one-hour telephone notice shall receive credit for each day of such availability towards their jury service obligation, but they shall not be paid unless they are actually required to make an appearance.