Systems and methods for optimizing usage of an available bandwidth for VoIP communications include a communications system, such as the Internet, for carrying the VoIP communication signals. A switch and a bandwidth limiter connected to the switch restrict bandwidth usage by applications other than those required for the VoIP communications. In the system, a modem or other narrowband network interface, a router, a network adapter, and a VoIP element are housed as a unit. The switch turns “on” and “off” the bandwidth limiter, and the bandwidth limiter when “on” restricts bandwidth usage of the adapter. The communications system is a digital data network, and the modem accesses the digital data network via connection of the modem to the network. Features for emergency bypass and external power supplies are included.