Cell phones used to be an extravagance, but now they’re almost a necessity. The only problem is the bills can be real shockers.

Catherine Zeta Jones, Danny Glover, sneezing monkeys and dachsunds are all pitching plans. But they don’t pay your bills. The real question is, why pay more than you have to? All you have to do is examine your bill, minute by minute, to figure out which plan is right for you.

“I was on a 300 minute wireless plan. Some months I’d be under by 100. Did I get to pay less? No. Did I get to keep those minutes? No. But if I went over, slam, with a bill almost twice as high. Frustrating? Yeah.”

(From a cell phone commercial) $19.95, $29.95, $79.95: Whatever your cell phone rate plan, the minutes seem to slip away, the numbers never add up and the bill is always so much more than you expect.

“It was never $19.95. Never. Never,” says Eliz Eskeranli, a cell phone owner.

If you want to get rid of those month-end cell phone bill surprises, you’ve got to let your secret cell phone self out of the box and take a serious look at how you use your phone. Because if you’re not honest about how long you talk, it’ll really cost you.

“There’s a penalty for choosing the wrong plan. If you go over the minutes you need, you’re going to pay,” says Allan Keiter, of www.myrateplan.com.

Is it any wonder we have sticker shock? Many cell phone owners underestimate the number of minutes they use and conveniently forget when they call out of the calling area, not to mention all those directory assistance calls at a buck each and then there are taxes and fees. For Eliz, taxes and fees added up to more than half of her bill.

“Do you have a shared package?” says a Cingular store sales rep. “We do have plans of $29.99 or higher.”

With seven carriers and 132 different plans to choose from in Chicago, finding the right one can be mind boggling.

“I really don’t have a concept of how to find a plan that will work,” says Ellen Carr.

“To get the phone at the discounted rate, you’d have to sign a two year commitment from today,” a Cingular rep says.

Two years? Ouch. But if you cancel your plan and change carriers, you’ll be hit with a fee of $150 or more. That’s why it’s so important to choose the right plan to begin with. Don’t rely on your sales rep to help you wade through the terms, conditions and legalese in your contract. That’s up to you.

“That factors in things like coverage and roaming and long distance and kind of factors in everything that would affect the price of your bill,” Keiter says.

www.myrateplan.com can help. Input how and where you use your phone and the website spits back the top 10 cell phone plans for you.

“So they can go into a store or online armed with the information they need to choose the right plan,” Keiter says.

Before you sign on the dotted line, keep these tips in mind:

Carefully estimate your airtime. It’s less expensive to over-estimate than under estimate how much you’ll talk.

Where will you be calling? And from where will you be calling? Look for free long distance.

Focus on the plan basics. The color of the phone and the gizmos should be secondary.

Read your contract carefully. Here’s where you’ll find the details on penalties, taxes and fees.

Every carrier offers a trial period from 48 hours to 30 days. Use it.

And last but not least, if you’re not happy with your bill, call your carrier and make a change. Many companies will be happy to find a plan that suits your usage. But be sure to shop around a read the fine print first.