Avaya 5420 Features 7 line x 29 character display 11 Fixed Feature Buttons 24 Programmable Feature Buttons Message Waiting Indicator Two-way hands-free speaker and microphone Desk or Wall Mountable Integrated Headset Socket, 8 Personalized Ring Patterns, Hearing Aid Compatible Compatible with Avaya EU24, optional expansion module Compatibility The Avaya 5420 digital telephone is compatible with Avaya IP Office 3.0 or higher Requires an available digital station port IP Office R7.0 – IP500 control unit must be running full IP Office mode. Not compatible in Quick mode. IP Office R8.0 or higher – IP500 control unit must be running Essential Edition. Not compatible in Basic Edition.