In order to call or message people using voice-over-IP technology on a regular analog phone, you will need to get a VoIP adapter in most cases. This is necessary as old phone circuits, or Ethernet lines, use old analog technology to transfer voice calls. However in VoiP calling, signals are transferred through the Internet, which is a mostly digital technology. These adapters are usually connected to to the telephone device itself in order for the signals to be converted.
This voice-over-IP adapter is usually in the form of a small box. It has a power adapter, Ethernet port, and a couple analog phone jacks. Many businesses have switched to VoIP on their phones as it is cheaper and provides more efficient bandwidth. It is also cheaper in the long-term for some large-scale organizations, as the cost for the infrastructure is cheaper and multiple phone calls can be connected simultaneously, with no need for more phone lines. Some homeowners have also phased out analog telephone service out of their home and switched to voice-over-IP.

Many companies develop and manufacture these adapters. They range from to high-end to the low-end market. Some of the companies that produce the higher-end products are Cisco, Linksys, and Motorola. Out of the companies that make the lower-end products, there is Citel, ATCOM, and GlobetelX. The main differences between the high end and low end products is that they include more phone jacks, support WAN, fiber-optic Ethernet wiring, and more phone technologies. For home users, who do not need all of these features, it is best to get a low-end one, as they provide all of the necessary features, not ones you might not necessarily use.
 
A VoIP adapter is a must for using your analog phone on a IP-based network, such as the Internet. It gives you much more choices and the technology behind it is much cheaper than a regular analog network. VoIP also allows you to secure your phone calls, and can be used virtually anywhere in the world, with only a moderately fast Internet connection. These adapters are fairly easy to use, with no need for any software. All you need to do is plug your phone line into the adapter, and you are done with setup on your part.