I do the same thing, never give out my cell phone number. I don't use my land line, and the only calls I answer on my cell are numbers which I recognize. (Nasty Ex problems.)
There's also a number you can call, and if you want I'll see if I can find it, where you can have your cell # placed on a "do not call" list.
I already have my cell on the do not call list. but i dont think that people who want donations are effected by that though.