I'd introduce Voice Messaging
1 - Click to voice message someone from the phone dialer
2 - Talk
3 - Click Send
1 - Notification akin to text
2 - Listen / Look at the transcribed message
Calls are inturruptive in nature, this would be a non-inturruptive voice option.
Easy to re-record if desired
Voicemail is ANNOYING
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I know some tried this with proprietary solutions...but without global or at least platform level availability it was doomed to fail.