A method is disclosed for providing syntonisation, synchronization, position or some combination to a wireless base station, micro-cell, pico-cell, femto-cell or access point, by providing holdover backup in a GPS clock module via at least one interface between the GPS clock module and an external time or frequency reference. Switching between synchronization modes is designed to occur on the control side of the oscillator portion of the module rather than at the output of two oscillators. A corresponding GPS clock module apparatus is disclosed for providing holdover backup via at least one interface between the GPS clock module and external time or frequency references.