Ask HN: How is short code data handled?

I was in a conversation today about short code and it is something I've never learned about. It was a discussion of how to use it for interacting with employees in a large(ish) company and keeping them engaged with the brand. Anyhow, can HN explain to me how the data is handled. I understand the user will text the short code number, but what happens from there? How does their response get into a database and a response sent back if needed? Basically is there a standard for this or does each company hosting (if that is the right word) the short code have an API to tie into?