An analog telephone adapter (ATA) is a device for connecting traditional analog telephones, fax machines, and similar customer-premises devices to a digital telephone system or a voice over IP telephony network.
An ATA is connected between an IP network (such as a broadband connection) and an existing telephone jack in order to provide service nearly indistinguishable from public switched telephone network (PSTN) providers on all the other telephone jacks in the residence. ATAs are used by many VoIP companies selling a telco-alternative VoIP service, where the device is used to replace a user’s connection to a traditional telephone company. When sold in connection with a VoIP service, the ATA is often locked so it cannot be used with a competing service, and the user can only partly change its configuration. Some providers do sell devices that are not locked and can be used with any compatible provider. This type of service, which is fixed to one location, is generally offered by broadband Internet providers such as cable companies and telephone companies as a cheaper flat-rate traditional phone service.