The "Len" is the length of your extension numbers. By entering 7, you are saying that your extension numbers are 7 digits long. The "Ext" is the digits at the beginning of your extension numbers. In your example, this line would apply only to 7 digit extension numbers starting with 395. For example, extension 3951234 would match, any other extension that is not 7 digits long and does not start with 395 would not match. You need the trunk field filled in to determine what trunk group you want to send these numbers out on. The "CPN" is the digits you want to insert in front of the extension number. In your example it would try to insert 717404 in front of the extension number. For example, it would try to send out 7174043951234. However, the "Total" field says to limit the number of digits sent to 10, so it would try to send 7174043951.