But they are also very dangerous, especially in the hands of children.
In some ways it is good that teenagers have cellphones. Parents can see their kids go off to parties in the knowledge that the simple 30 second process of their son or daughter writing a text can let the parents know that she or he is ready to be picked up. In other words communication between parent and child of where exactly both are, how much longer they will be etc is much improved.
That's the main advantage, but it's pretty impossible to force a child to only use a cellphone to talk to their mum or dad, and that's where the potential dangers lie.
Often a sixteen or seventeen year old child can be bored and decide to send a random text to a random number. Don't believe me? I have anecdotal evidence that it happens all the time. My mate in Auckland received a series of texts from what turned out to be a bored and pregnant 16 year old girl. In the weekends with what was then free vodaphone to vodaphone texting he would receive a barrage of texts saying "what are u up 2?", "why won't u talk 2 me", "I'm watching NZ idol", "do u hav a bf?" etc. He responded to a few out of vague curiosity but soon became annoyed with the incessant texts, giving her the cellphone number of two others on vodaphone, who then became the recipient of these frequent messages. I myself once had a text from someone professing to be a bored 17yr old girl in the South Island.
My point here is that random texts can go to anyone: a grandmother walking her dog, a paedophile, just anyone. People with sinister motives could easily take advantage of the situation. Starting off just sounding friendly, to meeting up, to being kidnapped. And these youngsters are probably too naive to even think of the consequences of sending off a bored random text. And it's not just 16 or 17 year olds who might be doing this - it's whoever has a cellphone. And that may mean anyone over the age of about six.
Cellphones with young children is another sad indictment on society in our self obsessed world. Parents need to realise the many societal, biological and financial harms they inflict, and take a good hard look at not allowing a child to have a cellphone until a certain suitable age (14?). And also looking to minimise their use.