They used to have a contact book . Then it went away. Then some people found some hacks that made it work but that could break notifications in SHM. I think now it’s just gone.
Not sure why, it would obviously be a valuable feature.
You also used to be able to contact multiple numbers with a text by using the SMS IFTTT channel. Now they’ve changed that feature so it will only send to the phone associated with your IFTTT account. I think it’s also limited in the number of text can be sent each month. So that method that no longer works for most people . 