I once had a custom mobile app created for me by Zach. This was during early Startup Village days.
The app cuts a call in three rings and sends a message requesting to text. I also added a decision rule that I be attending to only the people that texted.
Observation 1: Fair number of people did text to inform why they were calling.
Observation 2: In every 10 calls, around 3 - 4 required only a brief text response if at all.
Observation 3: In every 10 calls, only 1 - 2 instances where I had to call back.
Observation 4: Almost all of them could wait.