A mobile communications system includes switching between communication paths based on the quality of service. A VoIP service is coupled to a mobile network and a wireless local-area network (WLAN) via a wide-area IP network. A plurality of mobile communications devices are associated with VoIP telephone numbers. A public switched telephone network (PSTN) is coupled to the plurality of mobile communications devices and coupled to the VoIP service. A quality of service server is coupled to the plurality of mobile communications devices via the wide-area IP network for determining the quality of data channels to a mobile communications device via the mobile network and to the mobile communications device via the WLAN. A voice call is carried over one of the mobile network, the WLAN, and the PSTN depending on the quality of the data channels.