If you are seeing T104/Trunk 4 or the like, then trunk is not receiving Caller ID from the telco. I would suggest contacting your carrier and have them check the lines. Most carriers just point the finger at your equipment, but a cheap test might be to run to Wal-Mart (or your favorite discount superstore) and get a stand-alone caller ID box or find an analog phone with Caller ID display and when the trouble starts temporarily unplug the line from the back of the controller and into the CID box. Also, since most CID boxes have an in and out, you could put it in line with the CO line and see if you are getting caller ID there. My guess is it will be bad there as well and this is a telco issue.