Have a landline phone? You might be getting ripped off.

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A New Jersey consumer telecommunications expert said the vast majority of phone bills are calculated incorrectly, and most customers are paying more than they should.

"About 90 percent of the time there is some type of error on a phone bill. It can range anywhere from services that you didn't order to services you're no longer using," said Tom Allibone, director of audits at TeleTruth, an independent customer alliance group.

Taxes are often an area where customers get overcharged.

"Taxes being improperly calculated is a very serious problem," Allibone said.

On average, Allibone said most customers are probably getting overcharged by 15 to 20 percent. He has seen some cases where consumers have been overcharged by as much as 80 percent.

One of the charges that is questionable is something called the inside wire maintenance fee. Allibone said it's a fee that consumers have to pay every month to cover repairs to the phone jack, but those repairs are almost never needed.

In addition to charging consumers for services they will probably never use, phone companies also will put charges on the bill that shouldn't be there in the first place, according to Allibone.

"It's not uncommon for customers to place orders and the phone company just puts that charge on the phone bill," Allibone said.

So why are phone companies making so many mistakes and miscalculations?

"They make a lot of money and they can make even more money. I think they are just motivated to bring in the maximum amount of revenue," Allibone said.

Adding insult to injury is the fact that there's not as much government control over telecommunications companies these days.

Allibone said oversight in the current deregulated marketplace has dropped significantly, and as a result there are more problems and issues of this type.

Is there anything consumers can do?

"Customers have to pay attention and try to read these phone bills. Read that bill, even if you don't understand everything that it says. Contact the service provider, have the bill in front of them and try to go through each line item," Allibone said.

He said it's important for consumers to get a breakdown of all the charges on the bill.

"What you want to do is try to get a breakdown of the charges in writing, in easy to understand English terms because the gobbledygook on our phone bill can be very daunting. Many times it's done in cryptic or abbreviated format that you literally need to be an insider to try to decipher what it actually means," Allibone said.

The bottom line, according to Allibone, is consumers need to take action if they think they are being charged incorrectly.