The most common analog adapter has atleast one telephone jack (FXS port) for connecting a conventional telephone and an Ethernet jack, which you can use to connect to your LAN port in your laptop. Using an Analog Telephone Adapter (ATA), you may very well connect a conventional telephone to a remote VoIP server. Using various VoIP protocols, you may have your ATA communicating with the remote server, encoding and decoding the voice signal by using a voice codec such as ulaw, alaw, gsm, ILBC and others.

What is VoIP? VoIP stands for Voice over Internet. You use your internet service for perhaps a monthly fee as a subscription to your internet service provider. You can send and receive as much data as you want on this service without paying any additional fee, especially when you have signed for a plan for unlimited use. This is not the case with your regular telephone, where you not only pay a monthly rental for each line that you have installed, you also pay for the calls that you make. Therefore, your telephone bill depends on your actual usage and your rental or rentals. With VoIP, you can send voice over the internet service that you are using. This voice is first converted into digital data and transmitted over the internet. By deploying suitable adapters, as discussed above, you can make calls over the internet which comes free to you.

ATA is a device that connects a standard telephone to a network or a computer system so that you can make telephone calls over the internet. Internet based calls, especially long distant calls are substantially cheaper than the regular calls. Further, ATA is much more cost effective than the specialised VoIP phones that connect directly to the Universal Serial Bus (USB) input of your laptop or computer system.

Most of the telephone jacks such as, RJ-11, usually comes with four conductors and may also be available with six. It is likely that this jack is used in your household or office phones. These phones are plugged into by ordinary wire which is not twisted, sometimes known as “gray satin" or "flat wire." The jack connects your telephone to the telephone company central office or to your private branch exchange (PBX) system by longer wires known as twisted pair.

There are several types of telephone adapters available for your required application. All of these ATAs provide you with connectivity between the telephone system and your computer or a network, with some of these performing analog to digital converstions and connects you to VoIP server, while others use software to do one or both of the tasks. The simplest one is RJ-11 type, which plugs a telephone and/or a fax machine into the USB connector in your computer, laptop or your handheld system. This type of ATA generally works in conjunction with software, typically a soft-phone program. The software acts like an interface between the telephone and the VoIP server, for digitizing the voice data so that it can be transmitted digitally over the internet.