A few folks in the polling and campaign business have noted that these Romney "push-polls" really aren't push polls in the classic sense. According to the reporting they lasted roughly 20 minutes. Or if they are they're being done in an exorbitantly expensive way. A push-poll has to be made to really large numbers of people to have any effect. So to be cost-effective, they need to be really quick. And they can be since you're usually trying to convey only a short-snippet of information.
So, "I'm doing a poll. Would you be less likely to vote for Tom Tancredo if you knew he kept a harem of giraffes?" Done, end of message.
Lasting twenty minutes, though it sounds much more likely that these really were intended to gather public opinion and, specifically, to gauge the effectiveness of certain lines of attack tied to Romney's mormonism.
At this point of course the story has taken on a life of its own. Romney struck so hard at McCain over the story that if it turns out that Romney supporters, even without the campaign's knowledge, were responsible for the call, he'll have a real problem on his hands.