If you want to keep your conventional telephone and still make calls over the internet, you can use a VoIP adapter. You can be attracted to do so for economical reasons, since a good quality VoIP adapter will be less expensive than a good quality VoIP phone.
A VoIP adapter is a small box with two sockets: one to plug in a telephone cord (for your conventional phone) and another socket to connect it to the internet. VoIP adapters are also called “VoIP gateways” or, simply “gateways”. Some VoIP gateways will let you connect to different providers, but you will have to program the adapter for each provider (usually, the provider will tell you which adapters can be used and how to configure it.) Other VoIP gateways will be already configured by your provider, but they will be ‘locked’ to be used with that provider only. That is way you can “we unlock VoIP adapters” in some advertisements. They offer to “unlock” a VoIP adapter that was bought second hand.
There are adapters that will let you connect Wi-Fi phones to them. Now, a Wi-Fi phone is a special kind of VoIP phone and can be expensive, but here is the good news: many manufacturers offer wireless VoIP adapters together with one or more handsets. The whole bundle will have an attractive price since it is consumer oriented, and you can use each handset as a Wi-Fi phone (that is, a wireless internet phone). Certain VoIP gateways are plugged into the USB port of your computer. You can still plug your conventional phone, but they require your computer to be turned on whenever you want to make or receive calls. The VoIP USB adapters are almost always manufactured so that they work only with a given provider, which is a very common practice: most VoIP providers in the USA that offer you a free USB adapter if you subscribe to one of their plans will offer you a locked USB VoIP gateway.
Several VoIP adapters are made for industrial use, and they are not very suitable for a consumer. They are expansion cards designed to be hosted in a desktop or server computer. At a first glance, some of them look like an old “modem”, but they are more expensive than a modem. You might see them out there while shopping for your device, so we are mentioning them on this article.