If the parents want them to have one it's not your business.
Our 10 year old has been wanting one for several years. We told her we'd talk about it when she turned 10.
To have a cell phone she has to exhibit responsibility. That means the cat is never hungry, never without water, never trying to find a patch of litter that isn't caked so she can go potty, her dirty clothes find their way into the dirty clothes hamper in her bedroom, her toys find their way to their homes at least once per week, and she works to be an active participant in the home by helping out when needed.
So far she's still working on that. Once she is showing she's responsible and can handle having a phone that won't be lost under a pile of laundry or lost outside in the sand then we'll look into the cheapest most restricted cell phone we can purchase.
Just to add...
Smart phones are dirt cheap and even free if you look around and try to work within your own cell plan.
When hubby and I were going to change providers we walked in to a U S Cellular store to view their plans and they had a buy one get one free sale going on for Christmas. They also had a LOT of smart phones on sale for $99. They also had some $100 rebate sales going on.
So, we BOTH got Samsung Mesmerize smart phones, both were $600+ phones. Each was on sale for $99. With all the sales we got we got both phones buy buying one for $99 and got one free then sent off the $100 rebate for each one. So we got two gift master card gift cards each for $100. We paid $99 cash and got $200 back, they PAID us $101 to take their brand new line of smart phones.
We have stayed with them through the years and have a good plan. We build up points every month and can use those points to get a new phone. Right now hubby and I BOTH have the Note 2 phones. We didn't have to pay a penny for either one. We used our points and got them.
So just because someone has a smart phone or an I-phone does NOT mean it's a waste of money, they could have gotten it for free or for a very reduced amount.