Looks like a SIP phone, that probably won't work directly on an S8720 without an SES (SIP) server for it to login to, and then you have to do all kinds of admin on the SES side and the CM side to create a local extension on the S8720 for it, with virtual station routing to the SES server (trunk group/UDP route/Off PBX station etc)
DO you have an AVAYA SES (SIP) external server? Don't thing the S8720 can run one internally, like the S8300 series can.
Mitch
Mitch
AVAYA Certified Expert