There is an awesome service given by the US government to their citizens. It’s called National No Call Registry. You can apply for your phone number to be unlisted from the database of annoying telemarketers. This service is FREE and will last for at least five years.
But there is also a free service wherein you do a reverse phone lookup. At www.findoutwhoscalling.com, you can know who these people are and why they are calling you. So the next time somebody calls you, there will be a great confidence the next time you chose to answer or not.