Add: Click on this button to add a VoIP telephone number, IP address or port number in the address table.
Change: Click on this button to change the contents of the address table. Click on the line where a change in the VoIP telephone number, IP address, or port number is to be made, then make the changes in the selected line.
Clear: Select the line to be cleared, and then click on this button to clear the entire selected line.
All Clear: Click on this button to clear all information in the address table.
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When specifying another gateway, enter a port number specified for the call (usually 1720).