It's a privilege. Personally my thoughts on it are before they are 18 if the kid wants a cell phone then they will be earning it either through a job or saving up via chores or whatever. Same thing if they want a personal laptop instead of using the family computer and really any piece of personal technology. It's expensive yes, but you can get cheaper plans with limited talk and text and older phones or payment plans on newer phones and it teaches them very early on the value of their money. I don't mind getting the kid a super basic phone that's only capable of dialing 911 and a few other numbers like mine and my work number or whatever in case of emergencies because those do exist, but that would be all it could do. No texting, no internet browsing or games, ect.
If they're paying for it at home I don't care what they do with it as long as they're not disturbing anyone else. At school it's up to the school - if their policy is no phones then that's the policy. If it's a thing where if you get caught with it it'll be taken away and a parent has to come with you to get it.....well, let's just say I'd let that teacher keep it a week or two just to get the point across, and of course I'd let the teacher know this was my plan as well. It may suck, I know it did when I was in school, but if it's the school's policy I can see why it's reasonable and it teaches them there are consequences to their actions.