Historically VoIP was born to enable PC-to-PC voice communications: a PC, a microphone and headphones/speakers were needed to place a phone call over the Internet.

In the last years, in order to widen VoIP popularity by making it more accessible and usable, new telephone devices have been introduced: they're similar to traditional cordless and can be connected diretcly to a PC (through a USB port). This way you can make phone calls as you're used to do with your traditional phone line. Anyway a broadband connection, a PC and a VoIP software are still required.

Recently VoIP can be used even without a PC. You just need to have a broadband connection and to subscribe to a VoIP service provider (ex. Verizion, Vonage,...): you can directly connect your old telephone to a modem/router (often provided by the Telco Operator) and start placing phone calls over the Internet at very cheap rates.
If you want you can even chose to keep your traditional phone line or adding a new VoIP one.

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