At what age does a child get ready for a smart phone?

I believe its totally each parent's prerogative when to give the child a Smartphone. In my opinion and experience, the child can be given a Smartphone around 11-12 years of age with few strict instructions. I gave my son his Smartphone when he was 11 years old. I had strictly told him that I will have the access to his phone, that he will behave responsibly in using his phone. Parents can install softwares so that the child doesn't view inappropriate content.