I'm assuming this is a credit card/bank/collection agency autodialer. They've already called 10 times Saturday morning 7/26/08. Since they don't have the courtesy to ID themselves or leave a message, I don't pick up the phone.
See the comments about Advanta on this page:
http://whocallsme.com/Phone-Number.aspx/9198722436#pZ_b1LkNXwwCohgjLrDn-5Q
Don't talk with these guys; it is doubtful it will help and you will only give them ammunition for further calls and harassment. Know and use your legal rights if you owe them anything.