An Internet Protocol (IP) telephone operates a communications uplink to a switch based on activity on a separate communications downlink (such as to a personal computer) to conserve power when possible. The IP telephone monitors the communications activity of a link partner on the communications downlink, and when the link partner is present and operating at a relatively high data rate, the IP telephone operates the communications uplink at a correspondingly high data rate to support the communications needs of the IP telephone and the link partner. If the monitoring indicates that the link partner has reduced communications activity (which may include becoming entirely disconnected from the communications downlink), the IP telephone transitions to a second operating condition to operate the communications uplink at a relatively low data rate, with a corresponding decrease in the power required for operation of the communications uplink interface circuitry. By this mechanism, the power required to operate the IP telephony system can be reduced to realize costs savings etc.