This is a difficult question. Many prep schools do not allow mobile phones for reasons of security and keeping focus on making the most of school life. Prep schools are all about being busily engaged in academic and extra-curricular activity, so mobile phones and computer games can be un-necessary distractions from this. I would suggest therefore that if your child’s school does allow mobile phones, you consider if having one is really necessary in your situation, for example it is the easiest way for your child to contact you, since you live overseas. Then you set clear rules as to its use, how often and when. Pay as You Go is always a better option than contract as it gives you far more control over the amount it is used.
Once your child reaches senior school, it is likely that a mobile phone will become a necessity so you can be sure your child is safe and has the means to communicate with you effectively regarding pick-ups from school sports matches etc. Ensure once again you have set clear rules as to its useage especially in the age of instant messaging and the Blackberry. Ensure your child understands why they have a mobile phone and that it is not merely a communication tool to engage with their friends or to download games apps!