I've got a similar thing where I call another extension and ask to speak to myself. When the person who answers comes to tell me that I have a phone call, I tell them I'm on the phone and ask them to take a message for me. When they pick up the phone to take a message (from me, to me) I just tell them I'll call back later. Then I do call back...a lot.
my solution is to sit and ring every extension in your office, one at a time... and only let it ring once, and then hangup. Once they get mad enough... let it ring til they pick up, yell an explitive, and hangup. rinse, repeat.