Should children under 13 have mobile phone?

I think that children under 13 should have their own mobile phone, becase it can be useful in certain situations. Having a mobile phone just to enjoy it is not the best solution, but parents can be more relaxed, because they could phone their children at any moment, and know where they are, and what they are doing. Of course, children could be calling their friends all the time, and it can be dangerous, as it could turn into an addiction. But I think that education is what matters, so parents should teach their children the way to act and how to take control of it.