ATAs - Telephone Adapters
ATAs are Analog Telephone Adapters. They allow for you to convert analog telephone lines, telephones, fax machines and other analog based telecommunication devices or services to VoIP / SIP based protocols. You can then use older analog devices and lines with-in a VoIP/SIP based network with IP-PBX Phone Systems and other online services.
An ATA is technically a remote based server which functions as a bridge between old POTS / PSTN telephone line services, as well as older telephone cable wired hardware devices.
An ATA is connected between an IP network (such as a broadband connection) and an existing telephone jack in order to provide service nearly indistinguishable from public switched telephone network (PSTN) providers on all the other telephone jacks in the residence.