Or, increasingly commonly, "hashtag":
"What is the use of the hashtag(#) on a telephone?" https://answers.yahoo.com/question/index?qid=20130329025332A...
"How to play C hashtag minor" http://i.stack.imgur.com/S4pcU.jpg (via http://ux.stackexchange.com/questions/62190/)
As for "hashtag minor", it's a reshare of a second-person story, so I trust it about as far as I can throw it.
It's also used to check Verizon FiOS voice mail, where you enter it after entering your PIN.
As for the *, up until recently, I had a voice mail system where you used it if you were checking messages from a phone other than your own, to signal you'd be entering a phone (non-menu) number.
Haven't seen/heard of a use of * outside local PBX in years though.
Actually, rotary phones also worked like that. All you needed was something at the other end that could detect the signal -- called pulse coding, as opposed to the DTMF signal used by push-button phones. I worked with Dialogic boards in the 90s that supported both at the same time, so it was easy to create a PBX or menu-driven system that supported both types of phones.
It closes with a great quote that summarize the episode: "User friendliness has its drawbacks".