I guess this then highly depends on the country. For instance in Finland it's often vice versa: you can get a flat rate data deal, while the vast majority of deals have a per-message price for SMS/MMS (and MMS being higher in price). Which of course makes email/IM much more attractive than MMS usage. I for instance have a flat rate 3g data for 10 euros per month. SMS and MMS in general are liked by the operators because of their monetization opportunities: data becomes much more expensive when you turn that into 'MMS data'.