This paper presents a simulation-based optimization of signaling procedures in Internet protocol Multimedia Subsystem (IMS). The aim is to improve the performance of signaling procedures by applying an algorithm for Session Initiation Protocol (SIP) message classification and prioritization that is proposed in our previous work. This three-priority level classification of SIP messages is implemented in Network Simulator version 2 (ns-2). Its effectiveness is verified through the simulation-based study of SIP signaling procedures under different conditions. The simulation results are analyzed in terms of Registration Request Delay (RRD), Session Request Delay (SRD), and Session Disconnect Delay (SDD). These SIP performance metrics are improved if IMS is configured to process SIP messages using the proposed algorithm. Differentiated handling of SIP messages reduces the overload in IMS and thereby improves the overall Quality of Service (QoS). This encourages our next step in research activity, i.e., implementation and incorporation of SIP message classification and prioritization algorithm into experimental environment.