PhoneSpamFilter is the solution for blocking telemarketers from contacting your phone number. The site has a Windows-based software and API that does the telemarketer banning for you. Several users who have downloaded the software have reported significant deduction in telemarketer calls. The PhoneSpamFilter site also has a database of over 50,000 phone numbers so you could search for information about the phone number of the telemarketer who has recently bugged you.