Holding the build number 13C71, iOS 9.2 beta 3 provides new ways for developers to use Safari View Controller. In addition to mobile Safari changes, iOS 9.2 also adds support for AT&T's WiFi calling for iOS and OS X.
Apple's beta updates rarely consist of new features or user interface changes from previous betas. We assume that iOS 9.2 beta 3 is just an update with bug fixes and stability improvements, since nothing was announced in the release notes.