When they DO deign to leave a message, they state they are Kaiser and would like to tell me more about their wellness programs (aka you are fat, plz change that), and ask me to call them back at 1-855-471-6220. Ummmm how about NO. Could be legit, but I've asked while at Kaiser and was told they don't promote their wellness stuff by phone.
Just wanted to add, I have gotten calls EXACTLY like this before under a similar number; it seems like once enough people complain about it, whoever is really behind the calling will switch to a new number and start up again.