The way it works is teleamarketing companies needs to get this do not call list if they are doing business 2 individual customer marketing(B2C), before they call they have to check if the number exists in the database or not, if not found they can holler u. This is known and the fedral do not call list coz if you have signed up in this do not call list & have the money you can sue the company if they call u. Now remember sometime you do signup in free websites and checkmark on agree, In the terms and condition it will be mentioned that the phone will be used for marketing purposes. Please do read "Terms & Conditions",coz if you say i agree it is as good as signing on a paper so be careful and don't go after them coz you will be the one in trouble. However this rule dose not apply if your phone number is listed under Business, as there is no do not call list for businesses yet. How do i know this, simple i made a telemarketing software like a year ago. Have fun