I do understand it - you stick your own SIM card to a GSM modem and use this application to send messages via it.
I'm just contemplating that most providers would not allow endless one-way text messaging. Unless you have some sort of a business plan that allows this sort of thing.
Just looking at some use cases where this could replace Twilio/Nexmo but it seems like you would just get blocked by the carrier if you tried to send quite a handful of text messages.
P.S. I have nothing against the app and I think it's wonderful and I just MIGHT use it sometime if I'll need to send messages inside my own country. And I'll probably get blocked but it might just be worth it as I could just swap SIM cards as I could get 3000SMS for about 2.5 euros. But that's some black stuff happening in my mind now!