A modem translates information (binary data) from a phone or a cable line (analog channels), changes the data to a digital form, and delivers it to your computer.
While modems were created to be used on the traditional (analog) telephony network, you can configure them to work with VoIP (digital). Here are some troubleshooting tips to help ensure that your modem works correctly with VoIP.
To use modem calls over VoIP:
The other technique for handling modem calls with VoIP is called modem relay. In the modem relay technique (not supported by CenturyLink), a modem call over VoIP uses the VoIP device, generally called an analog termination adapter (ATA), to spoof a modem on each end of the relay. This technique is analogous to the fax relay technique for handling fax calls using VoIP.