This paper presents a new hidden data insertion procedure based on the estimated probability of the remaining time of the call for the steganographic method called lost audio packets (LACK) steganography. LACK provides hidden communication for real-time services such as voice over IP. The analytical results presented in this paper concern the influence of LACK's hidden data insertion procedures on the quality of voice transmission and the resistance to steganalysis. The proposed hidden data insertion procedure is also compared with previous steganogram insertion approaches on the basis of estimating the remaining average call duration. Copyright © 2011 John Wiley & Sons, Ltd.