What is That Sound?

The girls softball season is winding down quickly. Tonight's game ended with a blow-out win by the girls' team. When they came home, I suggested the girls call Grammie. The blond twin grabbed the phone and called Grammie.
The blond twin quickly became frustrated. She kept dialing and re-dialing Grammie's phone number. She kept talking about how the phone was making a funny sound. Eventually I told her to leave a message on Grammie's mobile phone. The blond twin left a message and went off to get ready for bed.
After she went upstairs, I tried Grammie's phone to hear the sound for myself. Grammie has had numerous phone issues in the past. If there was some real problem, I might have to drive to her house and let her know her phone wasn't working.
I dialed the number and heard the strange sound which frustrated the blond twin. It was a busy signal. Somehow the blond twin didn't know what a busy signal sounded like.
A while later Grammie called to say that she heard the girls' message. She had indeed been on the phone when the blond twin called. We laughed that the blond twin didn't recognize a busy signal. It was one ore sign of the generational canyon between us. In her always-connected world, she assumed that the only reason she couldn't reach Grammie was that the phone was broken.