BALTIMORE -- If your child has a cell phone, you have more to worry about than them going over their minutes, Baltimore television station WBAL reported.

The fancy ring tones that are a hot commodity with teens just might be the reason cell phone bills are high.

It's not enough for your children to have cell phones -- they want all the extras like wallpaper and ring tones to make their phones special. So when Gabrielle Barnes, 14, saw an advertisement offering ring tones from a company called Jamster, she jumped on it.

"It just said free ring tones," said Gabrielle.

But it wasn't free. Charges showed up on her mother's phone bill, and for months Kim Barnes wondered what the extra charges were for.

"I looked at my cell phone bill for this month and realized that there was an $11 charge for my daughter, $17 charge for my son," Kim said.

She contacted her cell phone carrier, Cingular.

"She explained to me that they are ring tone charges, but my children are telling me they're not downloading them," Kim said. "She said they don't have to they get their phone number in their directory and they keep sending them text messages and every time they open up their text message, it incurs a charge."

Internet postings show a lot of people have had similar experiences with Jamster.

The station reported that a California father filed a lawsuit in March accusing Jamster of luring his daughter into the service with false advertising. The suit claims the ads seen on stations geared to children offer a free ring tone, and the children respond and end up getting unsolicited text messages.

According to the lawsuit, the cost incurred is $1.99 for each ring tone, plus charges from the wireless carrier.

A spokesman for Jamster told the station by phone the company never advertised free ring tones on television and calls the lawsuit frivolous. The company also denied it targets young people with false advertising.

"It's obvious teenagers are heavy users of mobile content and that's why we clearly state in the he terms of service that subscribers must be of legal age in order to purchase a product, they must be 13 years and over and have your parent's permission," said Jamster spokesman Brian O'Shaughnessy.

Baltimore attorney Mike Oliver specializes in computer law. He looked at Jamster's online site, where kids can also download ring tones.

"You cannot enter into a contract with somebody under the age of 18 and have it binding or a short period after that, they can disaffirm the contract," Oliver said.

But unless you go over your phone bill every month, you may never realize you're being charged.

"I am very upset I was incurring these charges without notification," said Kim.

Jamster said it's working with the telecommunications industry to develop codes of conduct. But until then, Kim believes many other parents are unknowingly footing the bill.

The California lawsuit also names Cingular Wireless and T-Mobile USA. Both said they couldn't comment on pending litigation.