Young and mobile - should
Young and mobile - should we be worried: "It's exploiting children to make money. It's normalising and glamourising five-year-olds having cellphones."
Yet I remember exactly this from when I, and my sister, were children - and some of my 4-year-old nieces favourite toys include a (fixed-line) toy telephone, on which she enjoys long and fascinating conversations with her imaginary friends. I don't see anything unhealthy about children becoming acclimatised to telephone conversations (in much the same way that I doubt we'd see anything unhealthy about children learning about cars and playing with toy cars at an early age).
Communication is a pretty universal human drive, even at an early age...