IP telephony has many advantages over traditional PSTN telephony. These advantages are mostly manifested in the possibility of implementing many new services as well as in the network capacity saving. The focus of this paper is the IP network transfer capacity savings analysis. IP network completely replaces the PSTN network. Also, the influence of the voice activity detection technique and VoIP packet header compression technique on the additional saving of the required IP network transportation capacity is analyzed. The analysis is performed on the basis of the simulation measurements results which have been obtained by the originally developed application PlanVoip. The obtained results of the simulation measurements are presented in the analytical and graphic form.