DENVER -- Investigators at the Colorado Attorney General's Office are investigating phone calls that offer vehicle warranty extensions or debt consolidation. They are unwanted, unsolicited, and -- just maybe -- illegal.

"We do have several individuals working on this case -- one attorney full time. We've actually been investigating for about a year ... several different companies. Unfortunately, because of the way the telecommunications industry is this day, it takes a lot of time, a lot of legal work to figure out where these calls are coming from," said Nate Strauch, spokesman for the attorney general's office.

In just a few moments on the 16th Street Mall, several residents mentioned getting, and detesting, the solicitation.

"On a cell phone, it's pretty annoying," said Robert Richmond, a Denver resident tired of the calls. "It's a different number each time. At least, I haven't found consistency in the number -- maybe the area code is 712. I'm not too sure."

Actually, the phone calls come from area codes 702 and sometimes 305. These are numbers registered in Nevada and Florida, respectively.

But tracking them back to the actual person or company can take three or four subpoenas.

"We believe that a good portion of both of those calls comes from, interestingly enough, former mortgage brokers who've been put out of business and are now moving into this new, less-than-reputable business," Strauch said. "We're currently working with 25 other states."

They also want to work with people who are ready to complain about the calls. Those complaints must be made online.

You can register both home and cell phone numbers on the "no call" list, and so far 3.5 million Colorado phone numbers are signed up.

The question the attorney general will try to answer is whether these calls violate the state's no call list or involve scam artists trying to sell you bogus services.

Strauch believes that, ultimately, the federal government and the FCC will have to provide a lasting solution.

A Verizon Wireless representative reached on the mall Tuesday told 7NEWS you cannot block a particular number on your cell phone.