The next iteration of Windows Phone will no longer require three buttons on the front of devices, instead coming with support for on-screen buttons. Another major addition is support for dual SIM capabilities - this means that the rumored dual SIM Nokia Lumia 635 / 630 could be launched shortly after WP 8.1 is released. Microsoft worked with Qualcomm for a seamless dual SIM integration with Windows Phone. There will also be new Qualcomm chips supported, including the Snapdragon 400 and Snapdragon 200, both being perfect for ultra-cheap smartphones.
The new version of Windows Phone will allow us to store apps on MicroSD cards - great news for devices with low memory.
The rumored Cortana voice assistant was not mentioned by Joe Belfiore, but that doesn't mean it won't come to WP soon.
An exact release date for the Windows Phone 8.1 update was not revealed, but "this spring" should mean in March, April, or May the latest. We’ll bring more on this as soon as we have new details.