The standard way to connect to the calling system is to use the computer for the data - the voter information on the screen and the responses you mark after the call - and the audio, using VOIP.  In some situations, however, you may not be able to use the computer for the audio - particularly if your internet bandwidth is limited or your internet provider blocks the VOIP connection.
You can use a telephone for the audio.  It can be a cellphone, a landline, or an internet phone, as long as the phone has a ten-digit phone number and can receive calls at that number.  To use a telephone for the audio, you will need to change a couple of settings.
At the agent login webpage, click on the Settings button.
Click on Use Dialback: Yes.  In the Dialback box, type the ten-digit phone number you want this computer to connect to.  Click on Save & Close.
With these settings, when the agent logs in, the system will call the ten-digit phone number as part of the login process.  Remember not to hang up the phone in between calls!  If you hang up, you will need to log in again.