I called the FBI shortly after 9/11, to let them know about the funky charges that showed up on my mom's telephone bill a few months before. The phone company called her to let her know someone was using her calling card--only she hadn't used her calling card. They called her on 2 or 3 occasions, telling her someone was using her card to call Africa. The problem arose when they billed her for these calls, and then kept billing her. (I guess the people in one department don't talk to the people in another department at the phone company.) Anyway, she got all that straightened out, and we all forgot about it, but after 9/11 the phone calls that showed up on her bill took on new significance. There were about 10 or 15 calls that originated from a number in southern Florida, right around that area or region where the National Enquirer office was that got anthraxed (hey, I made a new verb!), and there were a few to Ghana (I think that was it--it wasn't a terrorist "hot-spot" country like Kenya or Sudan, and it wasn't Nigeria), a few to London, and a few to someplace in Ontario (I can't for the life of me find the copies I made). I figured there was some fraudulent phone card scam thing going on, but hearing, as we all did, that the 9/11 terrorists were supposed to "use their own resources" to support themselves while in the U.S., the origin and destination of the phone calls might aid in any investigation.
So I called the FBI--at first they thought I was calling about the phone scam, but then they realized I was trying to tell them that the phone numbers might yield information. I faxed over the bill. I didn't hear anything for a few weeks, but then somebody called me back, and I had to explain the whole thing over again, and told them to call my mom. Somebody from a different FBI office eventually called her sometime after that, but we haven't heard anything about it since.
Maybe there was nothing to it...but maybe those phone numbers belonged to terrorists. I wasn't about to call the numbers myself to see who answered, and tip anybody off.
So it's no overreaction to call the FBI. That's how they get leads. Your tip might be a dead end....but maybe not.
My parents and I were visiting France about a month before 9/11. My parents were robbed by two Arab men in the Paris subway and lost their US passports.
Still gives me chills thinking they might have altered those passports to do something terrible.
You did the right thing.
Good.