A knowledge base article about Will Duo Mobile work with an international phone number? provided by the UC Berkeley IT Service Hub - Knowledge Portal
Yes. The mobile application will function properly on an international smartphone and with international phone numbers.
Tip for Travelers: Using the Push or Passcode features within the app is highly recommended when traveling internationally. These methods can function over a Wi-Fi connection and do not require cellular roaming or international SMS capabilities.
See also: KB0014340 - OFAC Duo Error: Access Denied in Certain Locations