Telemarketing is a very expensive way for a charity to raise money. Typically 60-70% of every donation is kept by the company making the calls to cover their expenses. For charities with Police, Sherriff, or Firefighter in the name that number is often much higher, with the telemarketing firm keeping 90% or more of every donation.
Never donate in responce to a phone call. If you like the charity find a snail-mail address and mail them a check.