1. How to sign up for Do Not Call
Joining the Do Not Call Registry is actually very simple. You go to the website https://www.donotcall.gov/ and enter the landline or cellphone number you want on the list. Note that fax numbers are governed under different regulations, so signing them up won't do anything.
After going through a quick email verification, you're done. You can also call 1-888-382-1222 from any phone you want on the list. That's all it takes, and your number stays on the list until you ask for it to be removed or you give up the number.
Warning: You might receive a phone call from someone claiming to work at the Do Not Call Registry or Federal Trade Commission. They'll claim your number isn't listed on Do Not Call and offer to sign you up. Naturally, you just have to provide some personal information.
This is always a scam. Just hang up.
2. What Do Not Call does and doesn't cover
Once you sign up, the Do Not Call list takes you off of for-profit business call lists, but it isn't immediate. Telemarketers only update their lists periodically, so the FTC says it can take up to 31 days to take full effect.
Tip: If you receive an unexpected sales call after you've registered your number, and it has been on the list for 31 days, you can file a complaint. Just go to donotcall.gov or call 1-888-382-1222. Be prepared to provide the date of the call and the company's name or phone number.
On the other hand, political organizations, charities and survey takers are still permitted to call you. Businesses you've bought something from or made a payment to in the last 18 months also have a right to call. When they call, however, just firmly tell them to take you off their list and they have to honor your request, although they might still try to talk you into reconsidering.