I have had two separate phones on my plan that were "signed" up for Snap for Mobile, one of which is not a Smart phone. ATT was gracious in quickly refunding the $9.99 charge each time, and cancelling the service.
As I have not personally encountered the app and/or link that people get that signs them up for automatic billing on their mobile account, I am curious to know more details. If anyone recalls what they were sent originally that initiated the monthly billing charges, please make a note here so I can keep an eye out in the future.
In the meantime, I have locked down all phones on my plan for any mobile charges without my approval.