New Castle, PA
It comes down to what the market will bear
I often hear how something doesn't cost the provider anything to provide it, and I have to wonder, why does that matter? Trade is based on something people want and how much they're willing to pony up for it.
The market for sms or mms isn't based on what it costs a cell phone provider to deliver it; it's based on how much in demand those products are and for what price. It doesn't cost a music content provider but a penny or two in bandwidth to deliver an mp3 to me (if that, even), but if I want the song bad enough to pay $1.29 for it, then I'll pay for it.