Someday, If you find that the telemarketer is calling you on behalf of a charity that you wish to support, contact the charity and find out how to donate to it directly. That is smart way you avoid having part of your donation taken by a for-profit company.
Then to conclude the 'When a Charity Calls' series, if you are going to take only one thing away, we hope it is: when telemarketers are involved between then just HANG up the phone!