I used long codes (short codes are expensive!), and I didn't do the marketing myself. It's basically a way for them to keep a list of customers, enable automatic signups by texting the number, etc. They write their own messages and send them out.
I'm not much of a salesman, but I was able to make a few sales, mostly to local places via in-person conversations.
Anyway, I have this software built and I'm willing to talk about moving it into other niches.