Voice over IP (VoIP) or IP telephony is a very popular way of communication not only for single users but also for big enterprises. Due to fast-growing wireless technology and ease of use of wireless networks, VoIP is now being deployed over Wireless LANs (VoWLANs). The main issues in communication of real time application on IP networks, however, are providing Quality of Service (QoS), security and capacity. Capacity planning is an essential factor to consider at the time of developing VoIP network. Wireless links provide different capacity due to multi-rate transmission that affects all active calls. This paper focuses on the capacity problem and attempts to determine the maximum number of calls the bandwidth can support in each transmission rate based on different speech codecs and packetization intervals. © 2011 Springer-Verlag.