DENVER -- A new product that allows a caller to change the number read on a caller ID can even allow the caller to alter his or her voice.

Consumer groups said the device could lead to very dangerous behavior, and give a deviant mind an opportunity to lie.

The calling cards are called SpoofCards. The top two SpoofCard concerns among consumer groups are identity theft and harassment.

Caller ID has become as much a part of our daily culture as the phone itself. Businessman Robert Jellum admited he could hardly survive without it.

"I use it to identify who I want to speak with in the middle of a busy day. It's critical," he said.

Susan Liehe with the Denver/Boulder Better Business Bureau warns of the problems that could take place if the caller is not who the recipient thinks it is.

"It could be fake. What we're aware of is there is software or a download where you can actually pretend to be someone you're not on the phone," said Liehe.

It's even got a name. It’s called spoofing. For as little as $10, Web sites such as SpoofCard.com will sell a calling card that lets a person disguise their number.

Instead of calling from their own phone directly to another person's, they call the SpoofCard number first, and can make it appear that they're anyone they want to be.

"Please enter the 10 digit number you would like to appear..." the recording says as it prompts customers through a very easy process.

Callers can also disguise their voices. So even if it's a man on the phone, a person could hear a voice that sounds like that of a woman.

"What I'm concerned about is someone who takes a call because they believe it's important and in fact, it's a scammer," said Liehe.

The owners of SpoofCard said caller ID is a convenience and was never designed as a verification method.

"Nobody should ever rely on caller ID solely and give information out just based on the fact that their bank showed up on caller ID," said a SpoofCard spokesman.

SpoofCard also points out, although controversial, it's product is perfectly legal, and popular among users like doctors and lawyers.

“They're on the road, they want to make a call, but they don't want to divulge their cell number. They put in the office number and patients or clients see them calling from the office," said SpoofCard CEO Meir Cohen.

But the BBB said it could lead to fraud, harassment, identity theft or a number of other crimes. A concern for anyone who relies on it.

"I think our message here is be aware that such a thing, unfortunately is possible," said Liehe. The SpoofCard company said it is willing to help prosecute any criminal wrongdoing associated with the use of its cards.

Here's the bottom line according to the BBB:

Never automatically assume your caller ID is legitimate.

Never give out information during a communication that you did not initiate.

If someone calls claiming to be your bank or credit card company, hang-up and tell them you will call right back on a number you know is legitimate.