ATA stands for analog telephone adapter, which is an electronic device that connects a traditional analog telephone to a voice-over-IP network. They come in a variety of types, some embedded into an Internet-access adapter, set-top box, or they can be stand-alone devices that plug into a local area network switch or router. They all convert the analog signals, both speech and call control or supervision used by traditional telephones into digital forms suitable for a variety of voice-over-IP protocols, such as the Session Initiation Protocol (SIP), and the Media Gateway Control Protocol (MGCP), to name the most common.
With an ATA you can reuse a traditional telephone with voice-over-IP.
Just like old-style telephones can use two different methods to dial a telephone number, namely rotary dialing (pulse dialing) and tone dialing (TouchTone), an ATA may support one or the other method, or both. Dual tone multi-frequency (DTMF) is the technical term for TouchTone signaling.
Most ATAs today do not support the rotary dialing technology anymore, they simply ignore the dial pulses sent from the telephone. To support this, which is what most telephone collectors need, you have to be careful when selecting an ATA. The choice is not great.
The alternative to selecting a pulse-capable ATA is to use a pulse-to-DTMF converter between the telephone and the ATA. Some choices exist, but it appears no one choice works reliably in all situations.
One of the easiest and most reliable choices is to buy an old residential/small business PBX system, such as the Panasonic KX-T30810 or KX-T61610, that are very popular with members on this forum. These can cost less than many single-phone converters, while connecting either 8 or 16 telephones, whether they use tone dialing or rotary dialing.