The Spectralink IP-DECT Server 400 is a SIP telephony solution that supports up to 30 wireless users and 12 simultaneous calls. It offers a scalable solution that can grow with small to medium-sized businesses. The single-cell version is easy to deploy with an intuitive interface, while the multi-cell version allows expansion to additional base stations and users. The system integrates with Microsoft Lync and supports various codecs and licenses to tailor it to users' needs.