Duo doesn't require usernames or passwords, not on your end nor on your friends'.
But Duo isn't yet without its faults or missing features.Audio-only or group video calls aren't yet possible, there's no web or desktop client, no multi-device support, and no way to share what's on your screen for example instead of what you see with your cameras.With just a couple of calls, Duo has proven to me that it can replace Skype on my phone and maybe even tempt me to use it instead of Whats App audio calls with certain friends.Not because I to see them while I chat with them, but because the simplicity is there and it's enough to make me think twice before opening either app.While using the app, I've found this interface intuitive and quite easy to get used to.
Duo might not do more than one-on-one video calls, but it has implemented the essentials of that pretty well with mute, multiple camera support, and even a viewfinder switch to let you gaze upon yourself for a while if you need to.
Once you've installed the app, all you have to do is agree to a couple of permission requests if you're running Android 6.0 Marshmallow or above, then type your phone number. Once the code is there, you're inside and looking at your own sexy (or not) face through the front camera window.
A verification SMS will be sent to your phone - these were not working worldwide the first day, but now appear to be - and Duo should be smart enough to pick up the code from the SMS and input it inside the app. If you've ever used Whats App, you'll quickly spot the similarities.
Once that foundation is built and trust is gained with users, I'm sure Duo will start adding more traditional options and filling the gaps for a more demanding user base.
Simplicity is the name of the game with Duo and that starts with the setup.
Once you've made a couple of calls, the bottom overlay will start populating with your most recent contacts. (You can't see me now, but you will in a while.) If you're a geek like me, the first thing you'll look for are the settings.