58% of all phones sold last year globally were feature phones. In many developing countries, this is an even larger majority. If your market requires you to develop for these areas, you need to develop with this constraint in mind. These phones use SMS and USSD as a user interface. SMS is a long standing technique for sending messages, and USSD allows you to send SMS like messages in a secure session. You should look at USSD and SMS as another UI and UX platform and treat them as first-class citizens.