A new USB feature for Windows Phone 8.1 has been revealed in a simple Bing search. Found in our forums by Manikanta R., the trick brings up a hidden USB menu that allows you to enable two new features, including ?Ask me before using USB data connection? and ?Notify me when I connect to a slower charger?.
Indeed, we can confirm from our unsanctioned ?early look? at Windows Phone 8.1 using a developer device, that these USB options were there under the Settings menu. They were removed (or hidden) in the reviewer build that we received and also in the Preview release.
Full story from the WPCentral blog...