An indicator of a channel capacity of a wireless link between a wired telephone and a wireless hands free device is measured. Based on the indicator of the channel capacity, a call server decides whether to route a call to the wired telephone. The indicator of channel capacity may be is based on measurements of channel capacity between the telephone and the wireless hands free device taken at different times and at different locations. The measurements of channel capacity may be used to construct a map relating physical location and time to channel capacity available between one or more wired telephones and wireless hands free devices. The available channel capacity can also be used to cause indicators associated with low channel capacity to be displayed by the wired telephone or signaled to the wireless hands free device.