Just days after Google started rolling out its new video calling app Duo, it has been revealed that the app will also support audio-only calling soon. The revelation came from the company's product lead for communication Amit Fulay. It's worth mentioning that Duo is already optimized for poor networks, capable of even switching to audio calling if connectivity is weak. However, it doesn't explicitly offer audio-only calling feature. There's currently no information on exactly when the feature will arrive as Fulay just said "coming soon." Source
Source: http://www.gsmarena.com/googles_new_video_calling_app_duo_will_soon_get_audio_calling_feature-news-20017.php
