Mitt Romney thinks Rick Santorum’s latest robo-call in Michigan against him is "outrageous," "disgusting" and a "new low" for the Santorum campaign, but robo-calls have long been and are frequently used as a political tactic in the days before primary elections.

Shaun Dakin, who created stoppoliticalcalls.org -- a nonpartisan and nonprofit website meant to elevate political discourse starting with the creation of the National Political Do Not Contact Registry, said robo-calls are a "study in chaos" and a cheap way for candidates to get their message across.

"They don’t do them because they work," Dakin said. “They do them because they can.”

Dakin said voters receive an uptick in the number of political robo-calls "the very last days of election" and once the election is over they disappear.

"They are really onerous to the consumer," Dakin said. "The bottom line is everyone has a phone."

Santorum is not the only candidate using robo-calls during this year’s primary elections.

In Florida, Newt Gingrich put out robo-calls accusing Romney of taking kosher meals from Holocaust survivors while he was Massachusetts governor. The state's senior citizens "for the first time were forced to eat non-kosher because Romney thought $5 was too much to pay for your grandparents to eat kosher," the robo-call said. It was later proved to be an intense exaggeration.

In South Carolina, Romney quoted Santorum in a robo-call endorsing him during the 2008 GOP primary campaign on Laura Ingraham’s radio show.

"If you're a Republican in the broadest sense, there is only one place to go right now, and that's Mitt Romney," Santorum is heard saying. Santorum said he was working on faith in 2008 that Romney was moving in a more conservative direction than his then-opponent Arizona Sen. John McCain. Today, not so much.

The Detroit Free Press reported that swarms of political robo-calls started infesting Michigan voters' phones on Feb. 22, causing an annoyance in advance of Tuesday's election.

University of Michigan Media Technology Professor Russell Neuman said candidates "want to get message out and robo-callers want to sell their services," but it often turns off voters, especially when the calls come during dinner time.

"It’s a little bit of a catch-22," Neuman said. "A mixture of persuasion and annoyance."

Little research provides evidence as to how effective political robo-calls are, but there is no doubt that they cover a lot of ground. According to a study done by Jason C. Miller titled “Regulating Robo-Calls: Are Automated Calls the Sound of or a Threat to Democracy” on robo-calls in the 2008 presidential election, a person can deliver close to 100,000 pre-recorded messages in one hour for about $2,000.

The Federal Communications Commission has clamped down on telemarketers with the Do Not Call registry. But politicians cleverly exempted their phone messages from the list. California is the only state to prohibit political robo-calls while Indiana and North Dakota have a few restrictions.

"Politicians do not want to regulate themselves," Dakin said, noting that his ultimate goal is to add political robo-calls to the Do Not Call registry.

For now, Dakin’s advice to voters on avoiding political robo-calls includes not "giving away more info than you need to" when you register to vote, using caller ID and getting technology that blocks all unknown phone numbers.