IP Phone 1140E software 06256CJ added in the ability to support USB "headset" devices through the USB port. This is also available on the IP Phone 1120E/1150E. It includes support for the HID (i.e. buttons) on the Plantronics CS50-USB, the Plantronics CS60-USB and the Jabra GN9330E USB. It also supports wired headsets via the Nortel Mobile USB Adapter and the Nortel Destop USB Adapter (i.e. the same adapters used with the IP Softphone 2050). With any of these headsets plugged into the USB port, you can answer/release/mute calls using the buttons on the headsts and without requiring any external "lifter".
As separately noted on this forum, you can also use a powered USB hub and the Algo 4900 USB Analog Terminal Adapter to use an analog phone/fax/TTD.