You can verify a phone number's validity before making a call, whether the number is listed on a paid lead form or written on the back of a napkin, or an unknown number on a caller ID. There are paid and free services that will complete a reverse lookup, checking the number's validity and listing the phone's registered owner.
Go to the Phone Validator website (http://phonevalidator.com/).
Enter the phone number in the "Enter Phone Number" box.
Click on the "Search" button.
Click on "Click Here for Results," next to the "Directory Assistance Results" column.
Review the results.