Keep one critical analog endpoint in service while your voice platform moves forward. The Poly ATA 400 is designed for straightforward SIP adaptation where a single analog phone, fax-adjacent device, or similar endpoint still needs to operate inside an IP telephony architecture. With 1 FXS port, it gives teams a clean path to preserve a legacy device without overbuilding the solution. That matters in remote offices, reception areas, temporary workspaces, and migration projects where replacing every endpoint is unnecessary or disruptive. The compact adapter format also makes it easier to deploy close to the device it serves. This type of ATA is often selected when reliability and simplicity matter more than feature density. It reduces the friction of mixed analog/IP environments and helps procurement avoid the cost of replacing equipment that still has useful service life. For organizations standardizing on SIP while protecting existing investments, the ATA 400 offers a focused, practical bridge.