I've been pondering this question for a while, and it's been seriously bothering me.
I have the following using my phone line.
-Honeywell LYNXR-2 Security System
-Panasonic 5GHZ wireless phone system with 5 handsets
Sometimes, when I call the house phone, it beeps and says "SYSTEM ENTER CODE". In other words, the call doesn't go through, and I hit something.
I've googled and googled this, but nothing has shown up.
Another note, is that when this happens, the speaker on the LYNXR gives a kind of pulse out. Not sure if that's relevant.