At a minimum, you'll need a connection to the internet. If your connection to the interent is through a standard dial-up modem, you will also need a computer in order to get online. Keep in mind that a dial-up connection, can only provide a maximum of 56 Kbps in bandwith, which limits the kinds of VoIP service you can use (a bit more on this later).

Ideally, you will have a broadband connection to the internet, often provided by a cable company, DSL or a T1 line. These kinds of connections usually provide plenty of bandwith, enough to be able to use any service there is. If you want to use your VoIP phone just like any other phone, it is best to have an "always-on" broadband connection: one where you do not need to log-in to be connected. If you have a broadband connection, adding a low-cost router or gateway can even turn an internet account that requires log-in into an "always-on" account, because the router or gateway ensures a constant connection.