A method for decreasing a Call Setup Time Key Performance Indicator (CST KPI) of an Internet Protocol (IP) multimedia call in a mobile telecommunications network includes: initiating the IP multimedia call from an originating user equipment (UE) to a terminating UE; transmitting a session initiation protocol (SIP) call initiation message from the originating UE to a terminating Proxy-Call Session Control Function (P-CSCF) through an originating Serving-Call Session Control Function (S-CSCF); and creating a wake-up message via a network element upon receiving the SIP call initiation message. The wake-up message bypasses a plurality of network application servers (ASs) to start switching a transition of the terminating UE from an idle state to a connected state before the SIP call initiation message reaches the terminating P-CSCF.