Automatic Call Distributor (ACD), also known as Automated Call Distribution, is a device or system that distributes incoming calls to a specific group of terminals that agents use. It is often part of a computer telephony integration (CTI) system. Routing incoming calls is the task of the ACD system. ACD systems are often found in offices that handle large volumes of incoming phone calls from callers who have no need to talk to a specific person but who require assistance from any of multiple persons (e.g., customer service representatives) at the earliest opportunity.

Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter - or microfilter - allows a single telephone connection to be used for both ADSL service and voice calls at the same time. Because phone lines vary in quality and were not originally engineered with DSL in mind, it can generally only be used over short distances, typically less than 4km.

Asynchronous Transfer Mode (ATM) is a network protocol which encodes data traffic into small fixed-sized cells. The standards for ATM were first developed in the mid 1980s. The goal was to design a single networking strategy that could transport real-time video and audio as well as image files, text and email.

An automated attendant (also auto attendant or auto-attendant, or sometimes autoattendant or AA) system allows callers to be automatically transferred to a user's extension without the intervention of a receptionist. A receptionist, who acts as the telephone operator, can be reached by pressing 0 on most systems. Although an automated attendant is usually a feature on modern PBX and key phone systems, it is possible to provide one on standard lines and phones.