The 944 is compatible with the AT&T 955 or 964.
NO KSU Required.
2 data ports
Page, intercom, call transfer
Compatible with 2.5mm headsets
24 number memory
Hold, do not disturb, mute, flash
Power failure operation for all 4 lines
Digital receiver, speakerphone and headset volume control
Selectable ringer tones
Hearing aid compatible
Expandable to 12 stations
A great additional item as an add-on to any 4-Line phone is the Intellitouch Music On Hold System W/ Adaptor (OHP6500) or the Intellitouch Music On Hold w/ CD Player NONPBX (OHP7500). Look under "Related Items" for more details.