Not going to tell anyone here how to run their life but it seems giving a 4 year old an iPhone is kind of unnecessary.
I agree, which is why she is only allowed to use it about an hour or two a week. It's really there so she doesn't break ours when we're out. Trust me, if it weren't free to us from a friend, she absolutely wouldn't have it. And, as I said, she can't make calls, and it's very strictly controlled. She won't have a true phone of her own likely until she's a teenager.