Tell them that for $10 extra per month, they can use the GPS in your new phone to track you all hours of the day and night and make sure you're where you're supposed to be, lol. Sprint and Verizon both have a service like this, I'm sure other carriers have something similar. I'm not even guessing at your age, but you probably think this GPS thing sounds like a bad idea... well it's probably something your parents would go for if nothing else has worked...

like i said HELP!! i can't convince my parents i need a phone, what might convince them? (they already have phones)