Thanks for asking. My use case is programmatic. I wrote a couple of ruby and bash scripts that automate a few different things. One is a poor-mans SMS scheduler that allows me to have it fire off at a set time. Another parses incoming messages and alert me differently based on content (matches against a set of regexes), and in some cases will auto-reply. Another, I had a case where I need to individually send out the same SMS to a couple dozen people. With termux (and ruby) it was trivial for me to script it up.
The possibilities are (or were) endless, which is what I love about a platform. I've always hated the UX of SMS, but people insist on using it anyway. At least this way I use it on my own terms.
You have to both `termux` the app and `termux-api` to get SMS functionality. I build both at the same version so there aren't any compatibility issues. Then make sure you don't have automatic updates turned on otherwise the Play store will "update" you to a non-sideloaded one that does not have the SMS ability.
I was going to say there must be apps that do this but it looks like Play store would ban those as well because they don't want apps doing that?
I think Google should subject power user apps to more scrutiny than banning them outright. If Android doesn't support things like these then it's no better than iphones.
I'm not OP, but for my part, I hardly ever use Termux with the on-screen keyboard. I hate typing on that junk. I carry around a small bluetooth keyboard, and I generally pull it out whenever I'm going to do anything with the terminal, or spend more than about 10 minutes using my phone in general.