Provide a value for this property only if you need a prefix in front of numbers dialed via a modem. It is a best practice to first attempt to use the dialing rules configured in Windows (in the Phone and Modem settings) for prefixing numbers to a voice modem. Only use this setting as a next resort.
Do not configure as a workstation-specific setting. This must apply globally.
This setting is for numbers dialed via a modem, specifically. If you need to prefix a number for Twilio or VoIP, see Application Configuration > Edit Properties (Basic) > Alarms tab.
Section: System
Default: ModemCallPrefix =
*No restart required (Settings.Dynamic property)
