Radio access technologies (RATs) selection algorithms have been studied in the literature and nowadays equipment with several RATs incorporated into it is already common. The major goal of this work is to measure the gain obtained by using WiFi as a backup network for HSDPA, allowing for preventing from quality of service (QoS) deterioration when in a low mobility scenario. Since IEEE 802.11e already supports QoS, it was the natural choice. The proposed RAT selection algorithm is based on the load of each system, and the results show a gain of 60% on supported network load with QoS over the HSDPA-alone system. As a consequence, when there is heavy load for the IEEE 802.11e network, acceptance of high priority services will affect the delay in low priority services, like FTP.