I'm building something in the same space [0], the landing page is outdated but the version in my head is similar to your idea, as a mobile app in Flutter with a Rust backend API, and Twilio for the SMS, calling, and emailing.
And good for you for cutting scope and just launching! That's what I did a few weeks ago, I built a site in 24 hours, launched it on HN and Reddit, and got 20k visitors in a 48 hour span after launching [1] because I was tired of procrastinating launching products. I also got a lot of really good feedback from the launches, so now I'm learning that launching early and often is key to iterative development.
Don't worry about the pricing by the way. I'm going to make my app cost $20 a month simply to weed out people who won't take habit formation seriously. Those that want to buy it will buy it and those that won't, well, they're not really worth caring about since they're not your customers anyway.