Solution: Kind of phone signal that's nearly obsolete - NYT Crossword

A “Kind of phone signal that’s nearly obsolete” is a BUSY signal, which (for you young’uns out there) is the sound you’d hear if you called someone whose phone line was already in use. This clue sent me down a rabbit hole of thinking about what else about phones could be considered nearly obsolete. For one thing, it is a little weird that the phone call icon on our cellphones is still an image of a hand-held landline phone! For another, we still say “hang up” to mean “disconnect from a call,” even though most people do not literally hang up a handset to end a call anymore. Is there a word for this phenomenon?