I installed this for use over a DSL enabled line. My 1st review gave this system only 2 stars since I got bad static, no caller ID, and only one ring on incoming calls. I have since learned that the culprit was a ComShare 750 phone/fax/modem switch incompatibility. Once that was eliminated, the jack system worked perfectly on both incoming and outgoing calls on my DSL enabled line. Sorry Southwestern for the earlier angst. This is a great system, certainly deserving of 5 stars.