OS wide support and functionality
Cortana should be available OS wide in any app. A button in the action center should enable/disable the OS wide mode. When it is disabled, the phone should work when it currently does (activate Cortana only using the tile or the search button.)
However, when the OS wide support is enabled, a user should be able to use voice commands on any app to do basic functions, switch apps, open websites, open unopened apps, do calculations in the background (and just answer). For example, I am reading a webpage and I remember I have to set an alarm, I say " Cortana setup an alarm for 6 am" and she will confirm the alarm using a toast notification. The whole thing should happen without ever opening Cortana (only in ther background.) Other example, I am texting with a friend and we wanna discuss a meet up, so I say, cortana how is the weather tomorrow? and she tells me the weather, the whole things happens while I am still in the messaging window. Also, basic functions supported by a particular app should be controlled by voice/cortana, like when I am reading a webpage, I say go back or go to home or search for something and it works without ever closing/minimizing the internet explorer window.