Hello!
I am 12, and all of my friends (including me) have mobile phones.
Well, as we go on a bus home and to school, it is best to have one in case out bus gets stuck (this happens quite alot).
Also, its fun to have a phone! they are getting so more high tech, you can play games, go on the internet, play music and so much more. Phones aren't just for calling and texting any more!
When me and my friends go up to the park, we like to call each other in case one of can't make it. I is also fun to text friends like 'Why weren't u at skul 2day', or if you wanna speak in private.
So it is actually very normal to have a phone at 12, and younger.
Also, if I am at the park, or up at the local shops, or at a friend's my mum wants 2 no where I am so she calls or txts.
Hope I helped!
EDIT:: I have a story. Not long ago, my mum was stuck in a traffic jam, and I had got off the bus stop, and made my way home. The door was locked when I got there, but luckily I ahd my mobile phone. I was able then to call my mum and ask for arrangements. They are not all bad, in fact EXTREMELY USEFUL.
I am a responsible 12 year old girl, and my mum told me I neded one becuase I am at that age where you start hanging out with your friends.
Another story was: On the way to school last week, there was a massive crash, so our bus couldn't move. We had to phone out parents to tell them and ask them to pick us up if possible.
That was all in a couple of weeks (both stories), so they are useful!