Avaya 1110 Fundamentals page 279

Installation and configuration
Figure 54: Avaya 1150E IP Deskphone connections
4. Install the headset. If you are installing a headset, plug the connector into the RJ-9
headset jack, and thread the headset cord along with the handset cord through the
channels in the stand, so that the headset cord exits the channel.
Although a handset cord channel appears on the base of the Avaya 1150E IP
Deskphone, the Avaya 1150E IP Deskphone does not support a handset port.
IP Deskphones Fundamentals February 2013 279