(BPT) – Has this ever happened to you?

You sign up for a great deal on wireless service, but when it’s time to pay, the numbers just don’t add up. That $70 service shows up on your bill as $80 or more, leaving you confused about how your costs have gone up without any warning.

Extra charges on your bill come from a combination of taxes and a carrier’s administrative charges. Some are mandated by government regulations, but others are fees applied strictly at the carrier’s discretion. One of the main challenges in understanding your bill is deciphering the language used to itemize these charges.

Some carriers now roll all of their fees into a single monthly charge rather than listing them separately. While this may make it appear that they have eliminated extra fees altogether, this is not the case. Chances are, regardless of how the numbers are presented, you’re paying for more than just your monthly service.

Not all fees are created equal

Obviously, certain taxes and fees are unavoidable, and even necessary. State and local taxes, the 911 fee used to fund access to emergency services, and payment into the Universal Service Fund to help underwrite rural and low-income telecommunications services, are all required by law.

But it’s those pesky, less obvious fees that you have to be especially wary of, as they drive your costs up in unexpected ways. Most major carriers have an a la carte menu of items that trigger additional charges, and you probably don’t know they exist until they show up on your bill. Beware of things like:

* Overage fees: If you use more minutes, text messages or data than your monthly plan allows, many carriers tack on an additional charge for every bit of extra usage. Ask your carrier how they handle this, and be sure to take advantage of free usage alerts, by text or email, to help keep you on track.

* Activation and device upgrade fees: You may be excited about getting a new phone or upgrading to a new one. But, be aware that your carrier may charge you $30 or more to connect it to their service. With premium smartphones already costing in the $650­–$1,000 range, this extra charge can be an especially bitter pill for many cellphone users to swallow.

* SIM card kit fee: It looks like a tiny, disposable slip of cardboard, but a SIM card actually contains a small chip that lets your phone communicate with cellular networks. By providing a SIM card, your carrier allows you to bring an existing “unlocked” phone onto their service. However, some will charge you $25 and up just to get one.

* Administrative charge: These are similar to regulatory charges, but more nebulous. They’re usually billed as fees to cover the costs paid to other carriers when talking to someone on a different network, but they can also be applied for a host of general reasons. For instance, some carriers apply them for costs associated with cellular site rental and maintenance. Also, these fees can, and do, change from time to time, so watch them carefully.

Change, for the better

So, what can you do to avoid falling into the bottomless fee trap?

You’ve already started here, just by learning what to watch for. If your carrier’s fees are too high, switch to one that offers greater value by charging fewer fees. Ask about this up front. Consumer Cellular, for instance, is a no-contract provider which, on top of low-cost monthly service, provides free activation, free SIM cards, and charges no fees for changing plans or for overages.

Every little extra fee adds up to a great big phone bill. Choose wisely, and you’ll avoid being a victim of “bill shock.”