Got a chance to pick up a UT880 floor model at a very reasonable price. Neat looking phone and features.
My question - which NEC systems is it compatable with? Any special licensing required?

This is out of a document for SV8100/SV9100 UT-880 MLC dialer with video set up guide. I have also seen a user guide for the SV-9300 system, so probably all of the SV series systems.
CONFIGURING SV8100/SV9100 TO SUPPORT THE MULTILINE
TELEPHONE APPLICATION
These instructions assume that the proper licensing has been applied to the SV9100/SV8100 to support multiline stations.
The following SV9100 components are required:
 GCD-CP10 with GPZ-IPLE Daughter Board installed
 System Version R1 License (0411)
 System Port License (0300)
 VoIP Resource License (5103)
 IP Terminal License (5111)
The following SV8100 components are required:
 CD-CP00-US with PZ-32IPLA/IPLB, PZ-64IPLA/IPLB or PZ-128IPLA/IPLB
Daughter Board.
 SV8100 R9 Enhancement license (0038)
 IP Terminal Advanced License (5111)
 One SV8100 MLC Mobile-1 LIC for each MLC Mobile Client

Thank you! I can definitely use it with my SV8100.