The method comprises: a) a calling terminal initiates a call to a called terminal satisfying a defined condition; if the call failures, entering step b; b) deciding if state of the called terminal satisfying a defined condition is changed from the state incapable of answering the call to the state capable of answering the call; if yes, then triggering the call-back service, and entering into stepc; otherwise, continuing to execute step b; c) initiating a call to the called terminal bound with the called user again, which satisfies the defined condition.