Not the person you're responding to, but aren't there service plans with unlimited texting and images? I'd definitely use this service if I could text.
Maybe another SMS service offers that? If so, I'd certainly consider SMS again.
One option would be to re-enable the SMS option for people who deposit money to cover the SMS fees. Mark them up 100% (so 2c per SMS or something) and you'll have a built-in profit margin.