Avaya IP Office 500 is a modular, flexible design. The 4 universal slots house interface cards (Digital stations and Analog devices), and each interface card can also support a 'daughter' card (4 analog trunk and 2 or 4 port BRI), this design approach ensures cost effective, smooth growth. IP Office 500 supports 2 to hundreds of users and up to 4 T1/E1 lines (96/120 channels), 32 ISDN BRI channels and 144 analog trunk lines are available. New to release 4.0 is SIP trunking (Session Initiation Protocol).

Customers can enjoy low-cost call services with up to 128 connections to Service Providers offering "SIP trunk services" (often including free site-to-site calling). A new feature key, the 'Smart Card' fits securely inside the control unit, reducing the risk of loss or damage. IP Office 500 provides up to 128 voice compression module (VCM) channels available in 32 or 64 channel cards (four VCM channels are included).