I understand where you're coming from. If someone does want to donate to a charity, make sure you do it as anonymously as possible! Never provide any kind of legitimate contact information or they will hound you like a swarm of mosquitoes.
I ran into this problem with Habitat for Humanity. Before Caller ID and when answering machines recorded on tape, a caller would call every day at about the same time and hang up at a point where my answering machine would run the tape to the end with nothing on it, preventing any legitimate callers from leaving a message. One day I was home from work early and at the time of the mystery calls the phone rang - it was Habitat for Humanity who I had donated to just a couple of weeks earlier. I made it clear that their calls were unwelcome, and lo and behold the "mystery calls" stopped.
NEVER give any charity your contact information! They will hound you day in and day out!
I called and got a recording for American Institute for Cancer Research. I pressed 1 for more information and then 3 to no longer receive their calls. I entered my number, it repeated it back and said Federal Law allows 30 days to remove the number from their list, but that they will try to remove it within the next several days. All of this was a recording. It's worth a shot to listen to the message when you call to see if you can speak with someone or be removed from the list.
202-495-7181 - has called both yesterday and today. I let the answering machine pick it up, but of course, they don't leave a message. Checked the company out at http://www.charitynavigator.org/index.cfm?bay=search.comments&orgid=3264 Typical solicitation call.