Check this out! I used JohnWPB's suggestion above and "attached" my pen to a motion detector (X-10 Model MS16A). I then placed this motion detector/pen combination in a small box so ambient light/heat would not trip the motion detector. I then placed my cell phone within a foot of the box.
I then created an event in Homeseer so when it sees the motion detector's ON signal it announces "cell phone is ringing". I then called my cell phone and it worked great! I now know when my cell phone is ringing anywhere in my home.
There are some limitations though. One is that the pen will light whenever the phone is engaged in a conversation or text messaging. This shouldn't be a problem if perhaps you place a time out on your script after it gets triggered as I doubt once you answer the phone, you would be in range of the pen anyway (sort of an advantage to its limited range). Also when you first turn your phone on, its "checks" for messages and will light up the pen. Again, shouldn't be a problem if your phone has already been on for a few minutes before you place it against your "box".
Nice thing is it will detect any cell phone so you could have a "staging" area where everyone places their cell phones after they come home.
Not a bad setup for the price of the components involved.