I never cheated at school, I was always present and mostly in time (unless I was beaten up by my mother) and mobile phones didn't exist back then.

Phones are not forbidden these days although at some schools they don't like it so the students have to deliver their phone (in a n envelope) to the first teacher they have a class with. Next the box with phones goes into the teacher's room (you know where to go if you want to steal phones and data). At the end of the day the students have to ask for their phone. If there's any delay they will miss the bus back home and can wait another hour.
Another negative aspect is that if there are one o3 hours the students have nothing to do and just stay (there are not even enough seats or public place to relax or make homework).
Do the students pay more attention during the lesson? No way. They do the same like we - students who felt bored because they couldn't follow the lessons or those too intelligent to hear the same boring riddle again - did. They draw, doodle, play word games, talk about hobbies, sports whatever. So there's isn't more interest only more disliking the school/teacher.
I would never throw a phone in a tree, it's way too expensive. I rather leave it at home.

I wonder how old you were/are and how about the rights of students or simply saying: yes I have a phone for in case of need (that's why I have it and my children as well).

Good luck with the contest/exam and all those things you like to achieve.

A happy Valentine's Day.