If you provided more info maybe someone could give you insight, if you are confused about charges I would use the live chat option or call and talk to customer care.
If the bill says "premium data fee", that's the $10 "smartphone fee" that was added to any new lines and upgrades a few months back. If it's a "premium service charge", that's usually a third-party service billing through Sprint for ringtone, horoscope, or wallpaper downloads, or "specialty chat lines".
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