I don't see that anyone anywhere said that they think you are a horrible mother; opinions about you never came up at all. What most of us have said is that we essentially agree with your DH re: 6 probably being too young to have a personal cell phone.
You said that your DH thinks she is too young, so I, (and probably many other people), read your post as "is she too young, and if she isn't, what can I use to convince DH that this is a good idea?" There is an implied internal debate about the decision in the way that the post was worded, and since you told us what her age was, I looked at the decision in those terms.
My response was meant purely as a decision-making exercise: "ask yourself in what situations she would need such a thing." Logically, if you can come up with some that are actually likely to happen *to her* at this age, then getting a phone for the child makes sense, but if you can't, then getting it does not make sense, and if so, perhaps your DH is right about it being too soon.
I personally would not invest that much money on a pure "want" for a 6 yo; it would have to be a "need" for me to justify the expenditure. Your mileage may differ, and that's OK; you're not me. However, since you want an age number for my child, I'll give you one: 9 (next school year, 4th grade). It will be a loaner for one week (my old phone, temporarily reactivated) while he is away at overnight scout camp. I doubt I will give him one full-time before he is 12, and perhaps not even then -- it will depend on what is going on in his life at the time. At the moment, the only interest he has in cell phones is the same one he has in any electronic device, "What games can I play on it?"
I should perhaps point out that no one in this family is a social phone-chatter; we use our phones only when we need to, and we keep calls short. I've made about 60 calls on my cell phone this year, and all but 4 of those calls lasted less than two minutes. *I* barely need to have a cell phone, and I'm 43.