W90DM VoIP SIP DECT multi-cell manager (requires at least two x W90B), connect up to 60 additional W80B base stations, PoE required, AC optional, SKU #PS5V1200US, supports up to 250 concurrent calls, up to 250 WP53H / W56H / W59R / CP930W / T41S + DD10K / T42S + DD10K. Note: In order to pair and work with the W90DM base station in a multi-cell environment, the W53H requires firmware version 88.83.0.90.rom or newer, the W56H requires 61.83.0.90.rom or newer, the W59R requires firmware version 115.85.0.20.rom or newer, the T41S + DD10K or T42S + DD10K require firmware version 66.84.0.125.rom or newer.