I advise you to susbribe to smart limits to limits sms usage and data usages and time of they can use the phone or put purchase blocker on their phones. if you're really worried. Just stop them from using the phone
Can u set parental controls to prevent them to looking at "inappropriate" websites on the iPhone? My son has the Infuse, and I tried to prevent him from looking at such sites by using Smart Limits, but it looks like That can't be done. ?