Y.C.
I think it depends on each family needs and believes. My kid has hers when she was 10, it has be very helpful for us, I have being late and just call her and tell her I was running late. She has stayed with my MIL and has call us if anything has happened like grandma getting sick.
My husband also loves that she has her phone because sometimes I don't answer mine so he calls her.
I have lost my phone and use hers.
She has gone to Summer camps and use it to keep in contact.
She has text her friends and help each other with school work.
Yesterday it was the first time she had to take the bus because my husband was stuck in traffic and nobody was there to drove her back (we only have one car) the bus stop at the front of her school and stops a street away from us, I stood on the phone with her the whole time....it was horrible fo rme but she was so proud,I don't think we will do it again in long but I was glade she had her phone.