Standard SMS plans usually have a human-typing-in-a-keyboard rate limit, around a handful per minute - you can manually try this, I've got blocked a couple of t

Standard SMS plans usually have a human-typing-in-a-keyboard rate limit, around a handful per minute - you can manually try this, I've got blocked a couple of times by spamming a friend with "a", "b", "c"... Were I work, we've implemented a couple of nation-wide general population surveys regarding non-communicable diseases (working with those countries health authorities, of course). For the actual surveys, we get SMPP contracts with the local telcos because of this limit (and to get a vanity shortcode, reverse billing...). We started thinking it would also be cheaper, too (due to the scale pricing) - but the human time required for working out contracts with developing-world telcos for a project involving state actors can easily counter that. The throttling is something we need to take into account for the tiny-scale pre-tests we ran (while working out the contract) using an SMS Gateway App[0] we've built, similar to the one from this thread. The main difference is ours uses a queue-based protocol to exchange messages with a controlling server. [0] https://github.com/instedd/mobile-gateway https://github.com/instedd/mobile-gateway