I've done something similar. I used to have a few Raspberry Pis with 3G modems attached to them, with prepaid SIMs that had "unlimited" SMS plans. It actually

I've done something similar. I used to have a few Raspberry Pis with 3G modems attached to them, with prepaid SIMs that had "unlimited" SMS plans. It actually did work for a while. The problem that you run into is that carriers rate limit the number of texts per minute that a particular phone number can send (this is a problem with Twilio too, but in that case it's much easier to spin up a new number).