Damn I got sucked in via Thunderbird University - I'm going to call and complain - this is a terrible representation of what seem to be top-notch schools.
This is a clearing house used by a number of universities for their on-line course sign up. They only call if you have given your phone number re an on-line program. They are not as good as dealing directly with each university as they are a sales based organization under the cover of education.
If you answer it, it is automated and gives you a toll-free number to be removed OR tells you to press one (I know this simply because this is the viocemail that I get, an automated line explaining this)