ATA (analog telephone adapter

ATA or analog telephone adapter will automatically connected to the when is it connected to internet.

I believe a phone adapter is used to place calls via the internet and/or through using things such as Skype with a cellular device. It basically connects a telephone line to a computer network. Check out this link: http://searchunifiedcommunications.techtarget.com/definition/analog-telephone-adapter

No, That has nothing to do with telephone. Thats a USB adapter.

The device is called an "ATA" (Analog Telephone Adapter). It converts your voice into data, and sends it across the internet, also decodes data sent by the VoIP network back into voice (so you can hear the person you called). You can buy ATAs alone, or get them from any major VoIP provider.

IP phones somehow are designed with built-in adapters making them VoIP service ready.