California Code, Public Utilities Code - PUC § 7939

(a) If the commission or an authorized federal agency establishes a process to ensure that telephone numbers can be allocated in blocks smaller than 10,000, the commission shall require that a telephone corporation return to the North American Numbering Plan Administrator blocks of telephone numbers for reassignment, in a quantity determined by the commission.

(b) The commission shall direct the North American Numbering Plan Administrator to seek the return of blocks of numbers smaller than 10,000 not in use. The commission, for purposes of this section, shall define “not in use.”