You can setup a VOIP extension or a physical extension. A VOIP extension is a soft phone running on a computer, and a physical extension is a regular landline or cell phone. For a VOIP extension, select Use Voicent RemoteAgent from the following dialog window.

It is strongly recommended to use Voicent RemoteAgent program to setup a VOIP extension. By using the RemoteAgent program, the person at the extension has better control over incoming calls, such as display calls in the waiting queue, hold a call, park a call, and answer a parked call. The RemoteAgent program can further direct the incoming call to a regular telephone, such as a cell phone, a Skype instance, or the computer speaker and microphone.

Only select Use telephone when a computer is not available for running the RemoteAgent program. The telephone number needs to be 11 digit for US and Canadian phone numbers.