[akalsey]

There's lots of do it yourself ways to do SMS. You can also grow all your own food, but grocery stores tend to be the more popular option.

Companies choose to work with an SMS provider because they don't want to have to solve uptime, scale, and service issues themselves.

When you're small, running your company on a web server under your desk connected to your cable modem probably works just fine. Doing the equivalent with SMS might make sense at that stage, too. As you grow, your needs change.

One thing to note is that in the US, "unlimited" plans aren't actually unlimited. Read the fine print on your contracts. Carriers define a limit to the number of messages they consider to be reasonable use. It's a soft limit, so they don't immediately block or ban you for going over once in a while. But if you do it consistently, they'll start to charge for the overage.