To be able to place or receive calls using VoIP, you need a hardware setup that will allow you to speak and listen. You might simply need a headset with your PC or a complete set of network equipment including routers and phone adapters. Here is a list of the equipment that is normally required for VoIP.
PS. Don't be discouraged with all the technicalities, because you won't be needing them all. What you need depends on what you use and how you use it.
VoIP Gateways / Routers
VoIP Gateways are the most common as they enable traditional / legacy PBX’s to become VoIP enabled devices. A VoIP Gateway is connected to a PBX (either via Analog, ISDN BRI, PRI ports) which takes the call, and converts the voice signals into data packets and sends it to the VoIP provider via your Internet Connection.
The existing PBX needs to have available ports (or licenses) to connect, and should be programmed for Least Cost Routing (LCR) forcing all calls to first be sent to the VoIP Gateway, thus ensuring Cost Savings against the other local connectivity.
Lastly you will need to have a Router with available ports to connect the VoIP Gateway. If you have an existing Broadband Service then you already have a Broadband router that the VoIP Provider may be able to connect to.
ATAs (Analog Telephone Adapters)
An ATA is commonly called a phone adapter. It is an important device used to act as an interface between an analog telephone and an Internet VoIP line. You don’t need an ATA if you are using PC-to-PC VoIP, but you use it use an existing Analogue telephone which you want to use in conjunction with your VoIP service.
The VoIP or Internet Protocol phone is another VoIP device that can be used. It looks like your standard telephone, but is equipped with Internet or Network wiring to make it VoIP capable. The IP phone simply connects to your computer's router, and you are ready to make and receive calls. Several types of phones can be used with VoIP, depending on the circumstances, your needs and your choice.
PC Handsets or Headsets
Handsets resemble telephones but they connect to your computer through USB or a sound card. If your computer has an Internet connection, PC speakers, a sound card, and a microphone, or USB port you have the capability to download available software and make phone calls from your computer (like using Skype). This typically isn't used for Business VoIP.