The people who pay for this will be the people who are protected by it, so the main use case could be around reducing support costs of password resets or something similar. End users don't reliably care enough as a group, and Relying Parties only see costs. The developing country angle invites scrutiny, as it's not a source of unsophisticated users, in fact if you want amazing hackers, go somewhere small hacks pay off massively because of currency differences.
So the user story needs fleshing out. A good example might be, an app for women in developing countries to prevent their husbands from stealing their phone minutes and/or wages, which has some horrific failure modes, but this is what we're into. The developing'ness piece needs a deeper story than "the poor."
So who steals the SMS OTP in these countries? Arguably if it's social engineering (or just threats) a duress key that mitigated the harm someone could do with the stolen OTP would be a better solution. What is the SMS OTP protecting? Is it bank accounts, what else?
For a security product, you need a) something worth protecting, b) a specific person who cares about it because they literally risk starvation without it, c) an adversary who wants it for a specific reason, and d) a set of controls that make that adversary find a cheaper thing to want.
What's your a-d? Is it compelling? (If your a. is a password, it's not.)
I'm asking because this is really interesting, and I also have a tool for generating these a-d models because they are called threat/risk assessments, which are basically inverted/sad-path business models where things go wrong, but it also generates criteria for security solutions. Nothing the a-d questions don't answer though.
Enterprise customers will ask you dumb versions of these questions that will waste a lot of time. You don't need to answer these here, but consider the exercise.