I'm one of them and I know many others from friends to family members to former coworkers, etc. While I imagine it's not the best financial decision they're making, there are plenty of ways phone companies make these phones accessible to lower income individuals (high payment plans, extended period plans, putting costs onto credit cards so that the individual deals with their debt on their own). Even lower cost plans like Cricket Wireless carry phones like the Samsung Galaxy S6. (Thanks for asking.)
Keeping a list and knowing caloric content of food are great ideas on their own but a list is only so helpful when you're constantly bombarded with commercials in the store and colorful products catching your eye. Knowing the caloric content of a food is nice until you look around that store and see that the high calorie soft drink is your only option in that particular store. As majorities of Hispanic citizens are likely to be low income to middle class as well as live in major cities where they rely on public transportation trips to the grocery store are likely to be far and few between.
An app that allows a shopper to plan ahead by putting together a list and gauging availability of each item in grocery stores that also compares the options between competitors (e.g. aldi vs. walmart) can help shoppers plan a list ahead of time, make one trip that isn't inconvenient on their limited time frame/public transit costs and limit obstacles to choosing healthier options.
As a side feature, a plus program that also includes store coupons and deals could make the app very enticing.