I just (~11:45 a.m. Mountain Time on May 22, 2013) received a phone call from a young-sounding man representing the "Campaign to Reform Immigration for America."
I was immediately suspicious because of the campaign's name, so I asked what person or organization was behind the call. The caller seemed not to know, saying only that he was calling from California.
He went on to tout the Senate Judiciary Committee's passage of the uselessly-amended amnesty/immigration-acceleration bill—my descriptions, not his!—and ask me to phone my senator (Max Baucus [D-MT]) and urge him to support "immigration reform." So my initial suspicions were well-founded.
With that I lit into him, telling him I'd been involved in the subject for 15 years, that the bill had nothing to do with reform but was simply an attack on the American people—comprehensive capitulation to Mexico and to the cheap-labor interests.
I added something I say only on rare occasions, that if he actually believed what he was saying, then he should be ashamed of himself. (Generally, I consider it unproductive to tell a person to be ashamed of himself, but I thought this case was an exception.)
Then as he attempted to go on, I shouted at him "SHUT UP! SHUT UP!" He fired back that I mustn't tell him to shut up and that I should shut up. Then he bid me good day and hung up.
I tried phoning back the toll-free source number (855-831-1088) several times, figuring I might help tie up their phones by so doing, but I met with only busy signals and the like.
If you're the recipient of such a call, you might try to engage in the kind of "teaching" dialogue that my anger short-circuited.
But this would likely be fruitless, anyway. So probably the most productive thing you can do is to be as memorably unpleasant to these callers as you can manage. Make them pay at least some price for their (presumably paid-for) perfidy.