Both in-game and dashboard voicechat and Party Chat will be powered by Skype, in both audio and video molds (no microphone or headset required, as the mic is build into the Kinect 2 that ships with the system. Surely you can use a headset if you want to however, I assume), and Skype has vastly improved the audio quality, audio processing and microphone configuration settings available, as well as the voice options available to gamers when it comes to voice and video chat.
And all of this Skype goodness is seamlessly integrated into XboxOne and Xbox Live, allowing you to chat at any time, either audio or video chat, as well as do so while using multiple apps.
And in a very big deal, XboxOne Remote Play Sessions via Skype where you can see the screen (and gameplay?) of your friends whom you’re chatting with may be possible as well on the XboxOne just like on the PC. Although that hasn’t been confirmed.
To quote Microsoft on Skype in an interview with Polygon:
“Skype technologies are used in Xbox One which improves voice quality during multiplayer game sessions. Skype can also be used to call any of your Skype contacts for voice or video chat exclusively or while playing a game. Additionally, we have improved the Kinect hardware, from microphone configuration to dedicated audio processing, which contributes to providing a high-quality voice experience whether you are chatting in a game or through Skype.”
All of these develops are great ones. Unless, of course, you don’t play multiplayer games or do voice chat like me! :P