The current 802.11 standard was not intended to be used for devices to access or jump from access point to access point.  That is where 802.11r comes in.  The current standards for wifi "takes around 100ms to associate, and several seconds to re-establish authenticated connections using 802.1x. That will drop a voice call." The new standard improves connection and authentication speeds to 50ms which is quick enough to keep a voice conversation when using VOIP.  The connection that your device has with the current base station maintains its connection until the next base station in the jump takes over.  This should be great in cities where city wide wifi is available, but obviously will take some time for hardware to come to market and then longer still for it to be adopted.  Now if they would only make a VOIP iPhone when this comes standard becomes standard in our everyday lives we will remain in bliss.(or not with current problems)