You'll probably be getting a lot of those annoying calls for donations during the month of December, especially at diner time. I know I get at least one or two almost every night at this time of year. I have a standard answer, "I never make a donation over the telephone." It's a good practice and will save you a lot of grief.
Many of these phone solicitors are scam artists. Some may actually use the credit card information to steal your identity - the worst of the bunch. Others are paid solicitors that give very little of the money they raise to the charities for which they call. In fact studies have shown that fundraisers for public safety groups are notorious for turning over as little as 20% or 30% of the money collected.
If the organization that calls you is one that interests you, take down the information and research the group yourself. Check out the group's website, but also check out the American Institute of Philanthropy's grading system. If the organization doesn't get an A or a B, look for something else to give your hard-earned money to.
The only exception to these phone call rules is if you know the caller and the organization. If you're already involved with the organization and you know their fund raising activities are legit, go ahead and make the donation if you want.