You could also use multiple phone numbers to send SMS to avoid SMS ratelimiting. FYI most carriers consider Person to Person messaging to be below 1 message per minute and run between 40% inbound to 60% inbound messages.
One thing to watch out for is some carriers like Cellcom if I recall sell unlimited texting plans that actually have a 20,000 message cap then $0.01 per message thereafter. A cousin of mine hit this about a decade ago as she was part of many MMS groups.
>FYI most carriers consider Person to Person messaging to be below 1 message per minute and run between 40% inbound to 60% inbound messages.
Yep, I've read into that a little. I wasn't able to find anything explicitly forbidding a service like this in their terms, although there's a lot of legal documents that carriers have so I could have missed it. I read that you should expect about 1 SMS/second on consumer carriers, but it seems like I'm able to get about 2-3 SMS/second in my testing.
I didn't know about carriers having an unlimited SMS threshold... I'll have to look into that, thanks for the heads up!
Also, Google Fi has unlimited text/call for $20/m. Their SIM does work with USB GSM modems.
Nevermind most GSM stacks crash when receiving/sending many messages quickly, they aren't designed for high throughput messaging.
Sending via a carrier's multi-device calling/texting option where you bypass their cell network and connect to their servers over the web, or using VoLTE or VoNR is going to perform much better than GSM