1. A method, embodied in a device including at least one processor and a computer readable memory, the device providing voice communications over a packet-based data communication network by: receiving a call request; determining whether the requested call would span a virtual private network gateway connecting a local network to an external network at least in part by comparing a current Internet Protocol (IP) address of a calling party phone to be used in the requested call with a local IP address associated with the calling party phone, and determining that the requested call would span the virtual private network gateway connecting the local network to the external network in response to detecting a mismatch between the current IP address of the calling party phone and the local IP address of the calling party phone; and in response to a determination that the requested call would not span the virtual private network gateway connecting the local network to the external network, increasing a size of packets used in the call.