I have been using it since last October on AT&T without an issue.are you personally using wifi calling? you mentioned above its flaky,
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Is your account postpaid? I received the same message when trying to enable NymberSync, AT&T said it was an issue on their end and support fixed within a couple of minutes.I appreciate the replys regarding wifi calling however I just tried enabling wifi calling to give it a try and it returns an error saying my account type does not support the feature so there's that.