You don't have to worry that the best solution, you can't do it. Just you try to open your heart and try not to use the phone if necessary. When you have free time, it takes time to be useful, such as do homework.You must set up rules within the classroom. if someone play phone while the teacher was teaching to seize the phone and money were 20 baht. After 1 hours give phone calls. To do this until one year. You will notice that I have been playing phone.