The interworking network of 3G and Wireless LAN (WLAN) increases overall system capacity and provides higher bit rates on hotspot basis. Most of the existing analytical models assume identical 3G/WLAN mixed cells and balance of call flow (i.e., number of incoming calls equals number of outgoing calls) between two neighbor cells which is contrary to the real scenario. Models do not reflect the effect of configuration of neighbor cells which is important for cell planning for a cellular operator. We develop an analytical model with non-identical mixed cells differing in respect of number of WLAN-hotspots and amount of traffic pertaining to different types of services. Our numerical results show that horizontal handoff traffic in a cell changes significantly if number of WLANs changes in neighbor cell. Conversely, horizontal handoff traffic does not change significantly even with the changing number of WLANs within a cell if traffic and number of WLANs do not change in neighbor cell. © Research India Publications.