i will not deny that i owe, however i believe the law states that such a company is to leave a message when landing at an answering machine. I've yet to hear one, only reason i know what it is, is from research on the number.
The law, Fair Debt Collection Practices Act, actually prevents them from discussing debts with anyone but the debtor without express permission. Thus they either do not leave messages or leave cryptic messages for a "personal business matter" with a name attached. The silly ones that use a recording that states if you are not "person's name" then hang up and then proceed to leave details on the debt on the answering machine assuming the non-hang up means the "person's name" is listening are in violation.