Modern dunning starts with smart payment-retry logic (varying card-network attempts, timing) and escalates through email → SMS → voice → human collection.
Voice dunning recovers 60–80% of involuntary churn (failed payments due to expired cards, billing changes) because most failures are administrative, not financial.
Best-practice dunning preserves the customer relationship. "hi, your card didn't go through, want to update it?". Rather than mimicking collections-agency tone.