Many kids and teens today have their own mobile phones to use for social, family, and professional purposes. Mobile phones are equipped to send/receive phone calls and text messages. "Smart" phones or PDAs and other devices also enable you to access the Internet, take/send photos/videos, play games, listen to music, use a calculator, alarm clock, and calendar, not to mention the thousands of apps that offer a growing array of services.
Text messaging has many functions, even those with a typical 160 character limit. By sending one text message to your Twitter account, you can immediately update all of your followers (those who have elected to receive mobile updates). Or, you can vote on your favorite American Idol. You can also send a text message to GOOGL (56656) with search queries, such as looking up the definition of a word.
Many teens use a mobile phone as a part of a family plan, where the bill is sent to one person in a household or family. However, teens are able to procure their own mobile phones without committing to a contract by purchasing a prepaid phone.
The function of mobile phones in our lives is likely to keep expanding, as mobile phone companies are looking to sell more goods and services through the phone, where the buyer would pay for the goods along with the monthly mobile phone bill.
Teenagers have previously lagged behind adults in their ownership of mobile phones, but several years of survey data collected by the Pew Internet & American Life Project show that those ages 12-17 are closing the gap in mobile phone ownership. The Project first began surveying teenagers about their mobile phones in its 2004 Teens and Parents project when a survey showed that 45% of teens had a mobile phone. Since that time, mobile phone use has climbed steadily among teens ages 12 to 17 – to 63% in fall of 2006 to 71% in early 2008.
In comparison, 77% of all adults (and 88% of parents) had a mobile phone or other mobile device at a similar point in 2008. mobile phone ownership among adults has since risen to 85%, based on the results of our most recent tracking survey of adults conducted in April 2009. 
The mobile phone has become a primary mode of socializing for teens and they will often avoid contact with peers that don't have mobile phones, according to a study by Context. 
And almost everyone, including those whom the Context study considers moderate cell-phone users, felt anxious during the "deprivation" phase of the study that required them to give up their phones for a few days.
Mobile phone use has several potential costs: financial, academic, social, and health.
Aside from using more minutes than allocated in your mobile phone plan, extra text messages (both sent and received) can quickly add to your bill.
Some schools limit or restrict the use of mobile phones. Schools set restrictions because of the use of mobile phones for cheating on tests, harassing other people, causing threats to the schools security, and facilitating gossip and other social activity in school.
Some teens text message so much (200+ texts/day) that they have developed physical symptoms, Texting Teen Tendonitis (TTT). So much texting can lead to pain in the hands, back and neck soreness from poor posture while texting, impaired vision, and, possibly, many years down the line, to arthritis. 
One study found that teenagers who excessively use their mobile phone are more prone to disrupted sleep, restlessness, stress and fatigue.  Another found that mobile phone addiction can result in psychological disorders. 
Because mobile phones emit electromagnetic radiation, concerns have been raised about cancer risks that may pose when used for long periods of time. The current consensus view of the scientific and medical communities is that health effects are very unlikely to be caused by cellular phones or their base stations. At the same time, cellular phones became widely available only relatively recently, while tumors can take decades to develop. For this reason, some health authorities have urged that the precautionary principle be observed, recommending that use and proximity to the head be minimized, especially by children. 
Parents and their teens need to negotiate what is an acceptable amount of time and money spent on mobile phones. When a parent gives their child a mobile phone, there is usually a monthly plan that provides a structure for how many day time minutes and text messages are available. If a parent is paying the bill, they have access to the mobile phone records, which tracks how often teens call and send messages, and to what numbers. Teens should know that parents have access to this information, and know their parents' expectations for acceptable use.
While the mobile phone bill provides some information about mobile phone use, other factors effect teens' experiences on the phone. Because researchers continue to study the harmful effects of mobile phone use, it's not always clear when a symptom can be traced to the mobile phone. A teen could become depressed, for example, for a number of reasons. The best way to recognize if mobile phones have caused any problems in your teen's life is to speak openly.
Mobile phones have an important function in many people's daily lives and it's hard for us to imagine curtailing our dependence on them. Therefore, it might not be advisable to ban your child's mobile phone, which could lead to social isolation. The goal is to establish healthy habits. Time spent on mobile phones, while useful and fun, is time not spent focusing on other important activities, such as studying, working, and improving mental and physical health.
It's important to recognize that although mobile phones provide us with the ability to seek social contact and feedback at any hour of the day, it might be a worthwhile idea to spend time "offline" and to realize that our time might be well spent alone. In the same vein, parents might rely to heavily on mobile phone to communicate with their children, contacting them too much, in the place of a face to face conversation.
If your teen is encountering problems from mobile phone use, a collaborative conversation about self-reliance and independence from socializing might lead them to seek activities that free their hands from their phones. Ultimately, decreasing mobile phone use might actually be a relatively easy fix to problems.
Some states outlaw using mobile phones while driving.
Most recently, New York City passed a law that fines people whose mobile phones ring in "places of public performance." 
Law enforcement and intelligence services in the UK and the US possess technology to remotely activate the microphones in mobile phones in order to listen to conversations that take place nearby the person who holds the phone.
- "Teens and Mobile Phones Data Memeo", pewinternet.org (Aug. 19, 2009)
- "She's Gotta Have It: mobile phone", wired.com (May 16, 2003)
- "Many Young People Suffer from 'Teen Texting Tendonitis'", associatedcontent.com (Jul. 22, 2009)
- "Excessive Mobile Phone Use Affects Sleep In Teens, Study Finds", sciencedaily.com (Jun. 9, 2008)
- "Mobile-phone addiction in teenagers may cause severe psychological disorders", news-medical.net (Feb. 27, 2007)
- "Mobile Phone: Privacy", wikipedia.org
- "She's Gotta Have It: Cell phone", wired.com (May 16, 2003)