This is a proprietary DECT phone that would connect with the main ATA for the VOIP phone service provider. This ATA will support 4 devices including the noted ATA. I only have a need for 1 or 2 HD3s, and the other ATA noted under devices will be for the fax machine allowing me to have one more DECT device to plug into. Since I don’t need anything significant, this setup will work just fine for my 412 number.