Do you have 6 Line ports (jacks) on the side of your KSU? If you do---then you just take a mod plug out of one and switch it with another. For instance...Line 1 shows up on your phone as the first Line. If you switch line one and line two at the KSU---your first line button on your phone will NOW be actually the 2nd line. That's the way the lines---or the ports---can be tested. If the problem follows the line---then it's a line problem--if it stays with the port--then it's a port problem. Good Luck

Rockford VoIP