Think back to the moment when you picked a mobile-phone calling plan. It probably promised a low monthly rate and lots of perks, along with a flashy phone that took pictures and calculated your restaurant tip. In your excitement over being able to call your cousin Gertrude anytime, day or night, free of charge, you may have forgotten to ask about the fine print.

In fact, you may not have even thought about the fine print until you got your first bill -- and discovered it was a lot more than you expected.

Alas, the advertised rates don't tell you the whole story. Cell phones carry lots of extra charges that you probably don't think about when you sign up for service. Let's review some of the things you can expect to see on your bill.

Monthly calling plan
The first thing you'll probably see is the monthly charge for the plan you chose when you got the phone and service. You'll probably have enough options to make your head spin once you shop around. The plans will vary not only by the price and the number of included minutes, but also by rates for calling at different times of day. Make sure to be on the lookout for one-time costs, such as activation fees and early-termination fees.

Usage charges
Lots of perks might be included in your monthly calling plan, like free calls to friends and family members who are on the same network, or unlimited-long-distance allowances. But unlike with smorgasbords, you probably won't get a little of everything in your monthly plan. You might be billed extra for sending text messages or photos. Look in this section, too, for the fees that tell you whether you've exceeded your monthly allotment of minutes or made "roaming" calls outside your home network. If you're consistently incurring these charges, it might be a sign that you need to change your plan to more closely match your calling patterns.

Taxes and fees
This self-explanatory category will differ according to whether your state or local governments impose a tax on your service. You might also see 911 surcharges to provide emergency call service.

The items in this category might sound like taxes, but technically, they're not. These fees can be a little murky, so check with your cell-phone provider to find out what you might be charged. Here, you'll probably find the federal universal service fund charge, a payment required of phone companies to make service more widely affordable. It's almost always passed on to consumers. A search of the websites for some major service providers turned up some small fees, often described as covering the company's regulatory costs:

  • Verizon (NYSE:VZ) says it charges three small monthly fees -- a federal universal service charge, a monthly regulatory charge, and a monthly administrative charge.

  • AT&T (NYSE:T), which recently acquired Cingular, imposes a regulatory fee to defray its costs for complying with state and federal telecommunications regulations, in addition to a gross-receipts surcharge, and state and federal universal service charges.

  • Deutsche Telekom's (NYSE:DT) T-Mobile collects a fee to defray the costs of regulatory programs and other government obligations.

  • Sprint Nextel (NYSE:S) imposes fees that include a universal service charge, cost-recovery fees, and state and local fees that vary by area.

If you look at the fine print, you'll see that all of these charges are company fees rather than taxes.

What does all of this add up to? A lot more than you probably expected to pay when you signed a contract for that reasonable $29.99 per month. When shopping around, ask how much you can expect fees, taxes, and surcharges to add to your bill. You'll save yourself a big surprise when you get your first bill.

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Fool contributor Mary Dalrymple does not own stock in any company mentioned in this article. She welcomes your feedback. The Motley Fool has a disclosure policy.