The FCC Telephone Consumer Protection Act of 1991 (TCPA--47 U.S.C.S. 227; 47 C.F.R. 64.1200), together with the FTC CFR enacted in 1995 (the Telemarketing Sales Rule or "TSR"--15 U.S.C. 6101; 16 C.F.R. 310), require all telemarketing companies to keep a company specific "Do Not Call" list, along with a written policy for its use. Being placed on the list is free to consumers, and can keep "existing relationship" creditors (credit card and car loan people) as well as cold-callers from calling. These federal rules apply not only to residential lines but to all telephone lines.
To take advantage of the protection provided by these regulations, just say to the caller: "Do you have a do-not-call list?" Any interstate business will say that they do, as will many of the larger non-interstate businesses.
Next, tell them, "Please put me on your do-not-call list." Often, they will start to read a long policy script regarding calls in the next thirty days and the like. Feel free to interrupt and state that you have already heard this and are aware of it. Then tell them, "I have the following other numbers to be placed on the list," and give them any and all other numbers. Finish by thanking them briefly and hanging up.
Should a sales caller assert that they do not have a do-not-call list, ask them: "Are you aware that there is a federal law which requires all companies to keep a company specific 'do-not-call' list? Perhaps your legal department needs some pointers, and in any case, the FTC should look into this." Demand to get their name, their company name, their address, and the like, if nothing else, it will get them off the phone.
After about three months, you should notice a decrease in call volume, since it may take that long for the callers to rotate through their lists and get to you again, including the thirty day "grace period". Keep in mind, researchers/surveyors and non-profits are generally exempt, you may continue to get their calls.
Some states may have protections that are in addition to these mentioned above, and may complement those. For example, In Texas, telemarketing companies are now barred from calling consumers who have registered with the Texas "no-call" list. That system uses rolling registration periods for consumers, with an enrollment deadline and a later effective date. Here's the catch, the sign up fee is US$2.25 minimum for 3 years on a residential phone number; there may be other fees for other options and periods of coverage. The phone number is toll free 1.866.896.6225, have your VISA or MC number handy, or register online, http://www.texasnocall.com. But remember, the federal rules apply in any case, so take advantage of them.