by Larry Magid Most adults I know use their cell phones primarily to make calls. But ask any teenager and you'll soon find out that that's only one of many things they're doing with today's cell phones. One thing they're doing is texting. That's where they're using their thumbs to type out messages to their friends. The technology, known as "SMS" or "short message service, has been around for years and it's long been popular among both adults and teens in Europe and Asia. Text messaging started catching on with teens in the U.S. a couple of years ago and today it's pretty common to see kids thumbing their way through multiple messages wherever they are. Texting is also starting to catch on with American adults, though mostly young adults. It seems that the majority of mature Americans don't feel like learning yet another way to type. Still, if you have kids, texting may be the best way to stay in touch. The method of sending text varies by type of phone but typically you'll find a messaging icon on the phone's main menu, and sometimes you can send a message from the phone's contact list.

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If you have a Blackberry, Treo or other type of smart phone with a regular (QWERTY) keyboard, you may be able to use that keyboard to send text messages.

Texting using an ordinary cell phone keypad isn’t hard but does take some practice, since each numerical key is shared by three or four letters. To let the phone know which letter you want, hit the keypad once for the first letter, twice for the second, and so on. For example, to text the word “Hello” – you’d press the 4 key twice (to get H), the 3 key twice (to get E), the 5 key three times (to get L), then the 5 key three more times (to get the next L), and finally, the 6 key three times (to get O, and not zero).

Or you can use the T9 system that’s available on many phones. With the phone set for T9 you simply type 43556 (hello on the keypad) and the system figures out exactly what letters you want based on its predictive technology. Ever since I figured this out, I’ve been texting my son at college.

You don’t necessarily have to use your thumbs to communicate. There are a number of websites that you can use to send text messages to cell phones from a computer. All the major carriers have sites you can use to message their customers. If you Google “Send SMS to Sprint” you’ll get a link to that company’s SMS gateway. Replace Sprint with Cingular, Verizon, T-Mobile or any other cell phone company and you’ll find the right site.

If you don’t know what service the person uses, you can use smseverywhere.com to send messages to subscribers of Sprint, Verizon, T-Mobile and Nextel even if you don’t know which of those carriers the person is using.

If your kids are using text messaging, you need to talk with them about a number of issues. First, make sure they’re not spending their entire college fund. Unless they have a special texting plan, you might be paying as much as 15 cents for each incoming and outgoing message.

Most carriers offer plans for heavy users, which can save you a lot of money if you do a great deal of texting. Also, talk with your kids about etiquette and safety. They need to understand that texting is yet another way that people can get hold of them, harass them or engage them in an inappropriate discussion.

Just as with chat rooms and social networking sites, kids need to be careful about who they text with and what they say. They should never text about sex with strangers. Texting should only be used to communicate with people they know in the real world.

There are also other safety issues with phones these days. Many phones enable you to access social networking sites like MySpace and Facebook. That’s very cool but the same rules that apply to the fixed Internet also apply to cell phones. Kids need to know who they’re talking to and make sure not to reveal inappropriate information, including details that could help someone find them in the physical world.

And speaking of finding someone – there are now services that use the cell phone’s GPS features (put in cell phones so that 911 personnel can find you in an emergency) as friend locaters. If your kid’s phone is so equipped, make sure they use these services very carefully – if at all.

Loopt actually allows its members to be tracked by their friends. Helio and Telenav have services where you can send a message to tell your friends where you are at any given point in time. Be sure to read any safety advice that comes along with such a service and never send your location to someone you don’t know.

Today’s phones also have still and video cameras, which can get you into a lot of trouble if misused. Kids need to understand the privacy rights of others and should avoid letting other people photograph them in embarrassing or inappropriate situations. Remember, whether it’s posted via a cell phone or a digital camera, a picture is forever once it’s uploaded to the Internet or sent to other phones.

And just in case you don’t think cell phones are powerful enough, wait till you get a glimpse of Apple’s soon-to-be-released iPhone. With a larger than usual 3.5 inch screen, a virtual keyboard that pops up on the screen and a full-fledged Internet browser and full iPod capability, including the ability to view video, it’s really a personal computer for your pocket with all the benefits and dangers of PCs – amplified by the fact that you have it with you and are connected virtually all the time.

Another thing to be aware of: don’t be surprised to see “adult content” available on a cell phone near you. The CTIA cell phone industry association has said it is committed to providing parents with tools to filter such content from your kids’ phones. If you’re paying your kids’ phone bills, you certainly have the right to look at the details to know where they’ve called and who has called them, as well as other services they may be using.

You may also want to warn your kids about premium services that can really jack up the phone bill. “Voting” on American Idol and other shows can cost 99 cents or more per opinion and there are some services – such as ring tone downloads – that can cost several dollars.

There are still other ways for cell phones to vacuum up your hard-earned cash. A company in Bangkok, for example, is marketing so-called FlexiSpy software to “catch cheating wives or cheating husbands, stop employee espionage, protect children, make automatic backups, bug meetings rooms etc.”

I think I’ll pass on that one.