The issue regarding SMS Message Delivery on Duo deployments is fully resolved and all services are now fully functional.
Duo's telephony provider is seeing recovery on the SMS delivery degradation, and they have confirmation that customers are receiving SMS passcodes successfully.
We will continue to monitor the issue and will post any updates when the incident is considered fully resolved.
Duo is currently investigating an issue causing failures with SMS Message Delivery to some US numbers on all of their deployments. Updates will be provided as they become available.