Yup, that you do, and crazy it is. What you're supposed to do is get the unlimited text plan so that it doesn't matter. If you don't use SMS enough to justify the $20/month for unlimited, too bad for you (at least for AT&T I'm pretty sure it's unlimited or $0.25/text these days, with nothing in between). Or just do what I did and switch to T-Mobile.

There's fairly little spam, because the providers are happy to disconnect people for any sort of automation. So most companies are a bit skittish about taking on people that might be doing that, as they don't want to lose their connection.

In fact, it's a bit surprising Twilio's still able to offer such things. They routinely violate the rules that apply to the rest of us in the industry. Usually you've got to keep a 1:3 in:out ratio per number. Not sure what position Plivo's in. In light of the ratio requirements, maybe free inbound SMS is a way to help out on that.

Perhaps it's because they are paid for, but the US has remarkably little SMS spam.

If you're getting spammed you just tell the mobile phone provider and they remove the charges. In my experience it's pretty trivial to get large clearly repetitive charges removed.

We don't get much SMS spam in the US.