Dear Silvano, your doubt is not specified, what do you want to do? Want tips on where to start, how to do? How far do you know? This way we can help you better.
There are a few ways to do this:
1) Calling a web service / API (easier way)
2) Creating a server connected to a mobile phone, as you said it was in the cloud would be impractical.
Like this:
If your sms needs to have legal validity, which is now very high, you could try to hire Certising where you use the services of the company where Lleida.net works to send sms and certified emails .