Pound What?

Overheard in our car...
Blond Twin:  "Your phone is ringing."
Mom:  "Yes, I hear it. If it's important they will leave a message. I'll check at the next stop light."
A few minutes later
Blond Twin:  "Your phone is beeping."
Mom:  "Yes, I hear it. I'll check messages when we get to Grammie's."
Blond Twin: "I'll do it."
The blond twin grabs the phone and starts scrolling through until she finds my mailbox.
Blond Twin: "Ok, it's asking for your password. What is it?"
Mom:  "Press XYZ and then hit the pound key."
Blond Twin: "What's the pound key?"
Mom:  "It's on the lower right side of the key pad. To the right of the zero."
Blond Twin: "Mom, that's not a pound sign, it's a hashtag."
Mom: "Baby, it was a pound sign before it became a hashtag."
Blond Twin: "No one calls it a pound sign anymore Mom."
Brunette Twin:  "Back in the old days it was a pound sign. Now we call it a hashtag, so you're both right."
Mom:  "Nope. I'm right because I'm driving the car. Now, press the pound sign and find out who called."
Blond Twin: "Ok, I'll press the hashtag and get the message."