a simple google search results in many articles that state that in the US, the smartphone penetration rates exceeded 50% in August of this year
It is a deceptive comparison, because no one expects that someone is going to go out and buy a smartphone just to use the ISIS payment system, that would be insane.
But yet that is exactly what you are proposing in order to make your comparison.
Taking something you already own and adding a feature to it which costs no addition money is not a cost for that feature.
Your smartphones fees cover, voice text and data. At best if the ISIS system sends a few kilobytes of data during each transaction, you could add that extremely tiny portion of your data allotment to the price of using ISIS, but in reality it will be negligible.
People may choose to use it if they have a smartphone. It's not like credit and debit cards or cash are going away. They aren't marketing ISIS to non-smartphone users.
Finally, smartphones are a luxury item, no not everyone needs one, but I find mine extremely useful in my daily life and it makes my life easier. If something is worth the price is completely subjective, no one can decide for everyone else what is a justified expenditure and what is not.
It is true that you can pay extremely high rates for a family of smartphone users, but that is partially because people don't bother to look into their options, their are plenty of cheaper options than AT&T or Verizon. I myself pay only $45 for Straight Talk Smartphone service and for $45 a month the value I get out of my smartphone seems completely justified to me. Even if I paid $100 a month for my smartphone, if the price was worth it would still be a subjective opinion.
Also, I didn't tell those families that their kids need to have smartphones, in my mind giving your kid a smartphone and paying $80-90 a month for it is insane, I don't think kids need a smartphone, but if you've decided on getting them a smartphone, give them a cheaper prepaid option, like virgin mobile on $35 a month with 300 mins (most kids don't talk on phones anymore)