There are a few VoIP requirements that must be met before you can start using a VoIP service.
Broadband Internet Connection
VoIP requires a high-speed Internet connection. Depending on the VoIP provider, an analog telephone adapter (ATA) can require as much as 80Kbps of speed on the upload side.
Dialup connections are not suitable for VoIP for a few reasons. First, the connection is not fast enough to produce a clear telephone call. Second, because they are turned on and off, the phone, too, would always be turned on and off. It is quite obvious why this is bad. Lastly, you would need phone service with a local carrier so that your modem could dial out.
Almost any telephone will work with VoIP. However, because most VoIP service providers don't support "lighting up the house," expandable telephones are often recommended. With an expandable base phone, the main phone and base need to be plugged into a phone jack. The others simply need to be plugged into an electrical outlet. This makes it possible to put phones throughout a house when using an ATA with only one active phone jack.
If you do not use an expandable base phone, you have a few other options. One option is to use just one phone for your entire house. The other option is to use a splitter on the ATA device and run several telephone lines from it.
An ATA is a device that converts an analog telephone into an IP telephone. An ATA may , often times, be referred to as a VoIP Gateway or a TA. No matter the term used to describe them, ATAs all work in a similar manner.
ATAs convert an analog signal (voice) into a digital signal. This conversion is done using different CODECs.