An analog telephone adaptor (ATA) is a device used to connect a standard telephone to a computer or network so that the user can make calls over the Internet. Internet-based long distance calls can be substantially cheaper than calls transmitted over the traditional telephone system, and ATAs are typically cheaper than specialized VoIP phones that connect directly to a computer's Universal Serial Bus (USB) port.
Whether or not VoIP is cheaper than traditional phone service depends on a number of factors, including the rates charged by the respective service providers and equipment costs. Skype, one VoIP provider, offers free calling locally and between members, and inexpensive long-distance calls to other numbers.
There are several types of analog telephone adapters. All ATAs create a physical connection between a phone and a computer or a network device; some perform analog-to-digital conversion and connect directly to a VoIP server, while others use software for either or both of these tasks.
The simplest type of ATA has one or more RJ-11 jacks to plug a telephone (and/or a fax) into and a USB connector that plugs into the user's computer, laptop, or handheld device. This type of ATA often works in conjunction with some type of software (typically a softphone program). The software acts as an intermediary between the telephone and a VoIP server, digitizing voice data so that it can be transmitted over the Internet.
In an enterprise setting, an ATA usually has multiple telephone jacks and an RJ-45 connection to a 10/100BaseT Ethernet hub or switch, and is used to connect to a local area network (LAN). Such an ATA digitizes voice data, and uses protocols such as such as H.323 or SIP to communicate directly with a VoIP server so that a softphone is not required. An ATA that connects telephones to a LAN is sometimes called a VoIP gateway.
Some Internet telephony service providers, such as Vonage, provide an ATA to their customers as part of the service package.