Base stations in a wireless telecommunications network are calibrated to GPS system time by using position measurement data obtained from one or more hybrid mobile stations during regular position location sessions. Therefore, the calibration data need not be obtained externally from a calibration instrument, and the calibration may occur on a continuous basis to compensate for any disturbances or drift in the base stations. Privacy concerns are alleviated by using regular position location sessions that occur only when the operator of the hybrid mobile station places or answers a wireless telephone call. In a preferred implementation, the network uses Code Division Multiple Access (CDMA), and the hybrid mobile stations may provide Advanced Forward Link Trilateration (AFLT) or GPS position location data to the network.