Yes - that’s what a “Bulk SMS” provider gives you!
The ones I’ve looked at, you just pay “per message” - and it’s still significantly cheaper than SMS on a mobile tarrif.
Probably best to talk to a Bulk SMS provider; they do absolutely huge volumes so they’ll almost certainly get a better deal than you can get direct with the network…
Absolutely!!
There’s a lot to be found searching this forum for “Bulk SMS”; eg, fastract go can't conect more than 2 device in 1 pc - #2 by awneil
Unfortunately, all the links are broken: Lots of missing topics!
Here’s some I’ve used:
textmarketer.co.uk/sms-gateway.htm
intellisoftware.co.uk/sms-gateway/
dialogue.co.uk/
And some others I’ve heard of:
bulksms.co.uk/
esendex.co.uk/
shreeweb.com/sms-gateway/bulk-sms
And don’t forget that Skype can send SMS (and receive, I think) - and have an API.
Twitter?
No doubt there are specialists and/or special offerings for the “non-profit” sector…