There is an option of screening numbers that you do not want to recieve calls from. This is found in some handsets. For ex, the Nokia 2600 that I am using has this facility. Once you figure out the number, you can screen that number off.
These days people call for anything and everything.
On a lighter note, I had the following conversation with someone on my cell. The guy called me up.
Me: Hello.
Him: Is it wrong number?
Me: Yes.
He then hung up
