It's probably best not to even attempt to figure out how these people get your number. If you type it or write it on anything it's my opinion that it's only a matter of time before you get freak long distance calls.
Even worse on my cell just last week I got a call from a Vermont number that is supposed to be disconnected and suggested that my car insurance is about to expire. I don't own a car.
The weirdest thing is that I can't recall any time when I've given out my number except to friends.
My guesses are:
-that my number may have been given by proxy somehow by someone I know unknowingly
-they have a random phone dialer (Simpsons episode)
-some alternative source of phone records..
It's also too bad that none of the cell companies allow you to block numbers and bell or whoever makes you pay extra/month to be able to do it on a landline. Not sure how campus would handle it.
If you're curious about it and have caller ID, you can go to sites like
http://whocallsme.com/ or simply google "calls from 123-456-7890" to see if there are others who get similar calls.
I hope that's helpful and you are able to fend off the phone-bots.