Who's fooling your caller ID?

The number on your caller ID might not be who you think it is.

It's called "caller ID spoofing," and while it's perfectly legal in some circumstances, a number of high-profile cases have security experts asking if the law should be changed.

In 2007, a Mukilteo teenager was sentence to three years in prison for using a caller ID spoofing service to false report a hostage situation in Southern California. Swat teams showed at a home and scared a family who had no idea their phone number was part of a caller ID hoax.

The teenager tricked a 911 operator into think he was calling from the phone inside the home of the unsuspecting family.

That's an example of why critics of spoofing say it's getting out of hand. "As a consumer, you can't stop it," Paul Judge of Pinpoint Security told ABC News . "The best you can do is realize that's it's possible."

"It may be deceiving to put in someone else's number, but it's not a crime," says Meir Cohen, founder and CEO of TelTech of Tom's River New Jersey.

Cohen's company operates Spoofcard, one of the prominent caller ID spoofing service in the country. For a fee, users can cloak their caller ID to be any number they want. Users can also disguise their voice to be either a male or female caller.

"It's 100-percent legal as long as it's not used with the intent to defraud or cause harm," says Cohen.

Spoofcard promotes itself as a fun and legal way to pull a phone prank on someone, but Shannon Casad would disagree. Someone picked Casad's phone number to spoof. The scammer began calling people everywhere, and Casad's number was showing up in the caller ID. She said her phone ringing off the hook with angry call-backs.

"They said, 'Who are you and why are you calling me?'" Casad said. "Over three days, I had close to 100 calls from all over the U.S. and I obviously don't know any of these phone numbers."

Casad was forced to change her cell phone number that she had for ten years. There have been multiple attempts to ban caller ID spoofing but Congress compromised and President Obama signed a law the Truth in Caller ID Act of 2009 primarily to protect its legitimate uses.

"We have a lot of battered women that are using it to protect their phone numbers. We have a lot of law enforcement that use it to catch the bad guys," Cohen said.

The law make it illegal to knowingly transmit misleading or inaccurate caller identification information with the intent to defraud. It also bans telemarketers and bill collectors from using a spoofing service.

But the reality is, no one is policing caller ID services.

"There is no way to police it on an individual basis," says Cohen. "We are not going to make the internet illegal because somebody decided to do something illegal on the internet."

Cohen does admit there a few rotten apples who misuse the technology, like Paris Hilton. Hilton had her Spoofcard account canceled after being accused of using it to hack into voicemails. That's also how the English tabloid News of the World got into big trouble.

Many say hacking voicemail is all too easy with a Spoofcard.

Cell phones often bypass access codes and go directly to voicemail when you call your cell phone number using that same number. With that in mind, someone can set up a spoof card using your cell phone number and get direct access to your voicemail if it's not password protected.

Florida and Mississippi have tried to ban the practice entirely, but Cohen fought back in court and won. He has a warning to other states thinking about doing the same.

"We are confident that we have set a precedent in Florida and Mississippi for any other states that would think about trying to do the same thing," he said.

Cohen said his company hands over a user's call history to authorities if it gets a court order to do so. Anyone who feels they've been spoofed should register a complaint with the Federal Trade Commission.