They may buy lists of numbers from other companies, or they may generate their own lists by using automated software to dial random phone numbers. Sometimes, telemarketers will also receive your phone number from another company if you've previously given them your information for customer service or another purpose. You can lower the chances of getting calls from telemarketers by being careful about which companies you give your phone number to. You can also sign up for the National Do Not Call Registry, which will stop most telemarketing calls from coming to your phone.