A VoIP adapter is another term for Analog Telephone Adapter (ATA). An ATA is a hardware device that converts phone signals from an RJ-11 (phone) jack into VoIP compatible signals using an RJ-45 (ethernet) jack. VoIP adapters usually have a web interface. They provide initial configuration data through the primary connected phone using DTMF triggers. Nextiva uses the Cisco SPA-112 as it’s recommended ATA.