Here is why it is unlikely that Rudy Giuliani, Fred Thompson or any top-tier challenger to Mitt Romney had anything to do with the wave of anti-Mormon, Anti-Romney phone calls in Iowa and New Hampshire.
Think about the reward. Would the questions asked by the firm elicit any meaningful data for the campaign who wrote them? Would the relative reward of a few dozen voters changing their minds about Romney because of his Mormonism be worth the avalanche of embarassment and ill-will that would accrue to the candidate who authorized the phone calls?
Political consultants aren't stupid -- they understand that culprits eventually will out, that the profusion of citizen reporters and company moles virtually guarantees that the identity of the organization that contracted with the phone bank will one day be known.
Even if the goal is to earn media coverage by planting some audacious phone calls and then allowing the media pick up on them -- notice how the media coverage repeats the explicit anti-Mormon claims -- it's probably true that the sympathy that attaches itself to Romney washes out the reptition.
My guess: the responsible party is a free agent sympathetic to but not associated with a real campaign -- or an anti-GOP group testing messages -- or a dull party apparatchick who works for a small, inconsequential interest group funded by wealthy donors.