Various API that let you send SMS will make a call if the SMS can't be delivered, and then use text-to-speech to read the thing out to you. It's fairly obnoxious really.
And some, like Telia in Sweden, will keep calling until you listen to a certain percentage of the message to helpfully ensure that you've gotten the message. Which is loads of fun if, for example, someone sends you a link with a UUID--you basically have to pull the phone off the hook and let it finish before you stop receiving the calls.
(You can also contact your phone company and ask them to please remove this "feature" - but usually you have to be subjected to it before you know the phone company even does this!)
