I used to do phone collection from Australians Against Child Abuse and the Make a Wish Foundation...

It is hard, but I was never rude to anyone. There is a script you need to follow, they have pages and pages of comebacks for any negative response, but you only try one or two of them in any call. It is about guaging the person on the other end though - any indication at all of hope is a sign for you to keep pushing, gently!
It reminded me a bit of this in the JW door knocking thread - how Keike mentioned that even when a person says "no thanks" there is something that says "maybe..." and so they come back again. It is the same premise.
It is a sales job, so manipulation is key - not enough to rely on everyone's good nature especially when you have quotas to meet and $ targets per call.

None the less, you are already calling at the crappiest times of day, it is important to keep this in mind when deciding which tactics you are going to use to get the donation. And then there is getting the donation on a credit card Another manipulation in itself lol.