Well I just say, nope not interested and just immediately hang up, even if they're talking still. The only ones I entertain are the ones soliciting for donations like the Cerebral Palsy for kids, RSPCA and Kids Cancer Foundation, but anyone selling so and so gets the Im not interested, hang up routine.
Besides Im only donating if they send a letter ( so I can present that to my accountant for tax rebate later) I dont wanna give my credit details over the phone. Also with a formal letter I know Im getting it from a legal, existing group not some so and so claiming they're a whatever group. Besides I only donate a small amount anyhow. About the cost of a Deluxe, so its not so bad