With the aid of critical conditions including remaining power of a communication module and both an available bandwidth and a credit of utilizing communication functions of said communication module, and by cooperating with available network services of said communication module, a communication network currently appropriates for said communication module to be switched to is determined, for achieving an aim of retrieving network services and taking requirements of users into consideration simultaneously. Moreover, when there are no available network services for the communication module, said communication module enters a sleep state for about less than ten seconds, for preventing said communication module from consuming additional power or from bringing in unnecessary consumption in other aspects, where both the additional power and the unnecessary consumption in other aspects are caused from the fact that the communication module searches for available network services continuously.