Over dinner with my sister and her boyfriend, I was rattling off all the information that I had pieced together about these calls. It suddenly clicked with all of us that we should have thought of it WAY sooner than we did, since each of us was familiar with the responsible party.

It was a phone-enabled alarm notification from a water pumping station that my sister manages. We didn't know about this one, there were no alarms at the pump to indicate that it should be calling, it didn't speak a message indicating a problem like the other phone-enabled alarms do, and it continued to call after the alarm condition had been resolved. So, it suffered multiple failures and we're trying to track that down now.

So, now there's a $900 bill pending (according to my calculations). It's going to take some doing to resolve this peacefully, but I think it's possible.

Thanks so much for all your tips. I honestly wouldn't have gotten to the bottom of this without them! Ah, finally, silence in the house (except for the damn telemarketers, which finally pushed me to sign up for the Do Not Call list).