A hybrid navigation satellite receiver and mobile telephone combination, comprising: a GPS radio frequency and GPS-DSP processing stage for computing position solutions and accurate GPS system time; a mobile telephone transceiver and DSP processing stage for cellular communications; a master clock connected to independently supply local oscillator frequency references to the GPS radio frequency and DSP processing stage and the mobile telephone transceiver and DSP processing stage, and operating with power in the milliwatt range; a software controlled crystal oscillator model connected to correct the master clock; an accurate timebase connected to supply an accurate clock to the software controlled crystal oscillator model for compensating errors and drifts in the master clock by having access to computed GPS system time; during normal operation, the master clock uses milliwatts of power to operate, and is shut down when a user inputs a "power off" command, and operation of the master clock is resumed when the user later inputs a "restart" command; a GPS time regenerator for supplying a regenerated GPS system time by adding an offset count aligned to a last known computed GPS system time obtained before a "power off" command was input; a real time clock for generating said offset count during a "power off" period and for supplying it to the GPS time regenerator; and a 32-kHz watch oscillator disposed in the real time clock and for operating continuously with battery power in the microwatt range; wherein the accurate timebase device receives an offset count from the real time clock and supplies computed GPS system time to a GPS time regenerator during normal operation and feeds back a regenerated GPS time through the accurate timebase device to GPS-DSP processing stage after said "restart" command is received; wherein two crystals are employed, and communications reference frequencies are synthesized from GPS reference frequencies instead of being referenced by a communications-part voltage controlled oscillator reference crystal; and wherein, a complete shut down of both a navigation satellite receiver and mobile telephone in a combination are provided for during said "power off" period to save battery power. a GPS radio frequency and GPS-DSP processing stage for computing position solutions and accurate GPS system time; a mobile telephone transceiver and DSP processing stage for cellular communications; a master clock connected to independently supply local oscillator frequency references to the GPS radio frequency and DSP processing stage and the mobile telephone transceiver and DSP processing stage, and operating with power in the milliwatt range; a software controlled crystal oscillator model connected to correct the master clock; an accurate timebase connected to supply an accurate clock to the software controlled crystal oscillator model for compensating errors and drifts in the master clock by having access to computed GPS system time; during normal operation, the master clock uses milliwatts of power to operate, and is shut down when a user inputs a "power off" command, and operation of the master clock is resumed when the user later inputs a "restart" command; a GPS time regenerator for supplying a regenerated GPS system time by adding an offset count aligned to a last known computed GPS system time obtained before a "power off" command was input; a real time clock for generating said offset count during a "power off" period and for supplying it to the GPS time regenerator; and a 32-kHz watch oscillator disposed in the real time clock and for operating continuously with battery power in the microwatt range; wherein the accurate timebase device receives an offset count from the real time clock and supplies computed GPS system time to a GPS time regenerator during normal operation and feeds back a regenerated GPS time through the accurate timebase device to GPS-DSP processing stage after said "restart" command is received; wherein two crystals are employed, and communications reference frequencies are synthesized from GPS reference frequencies instead of being referenced by a communications-part voltage controlled oscillator reference crystal; and wherein, a complete shut down of both a navigation satellite receiver and mobile telephone in a combination are provided for during said "power off" period to save battery power.