When there's a big event happening while you're away from home, what apps do you use to keep track on your phone? Probably not Facebook -- it's often the last service to show you up-to-the-minute info. That might change after today. Facebook has started rolling out its Trending feature on mobile, along with a few upgrades that make it easier to see what others are saying about a hot topic. You can follow a Twitter-like live feed if you want to see reactions as they trickle in, but you can also limit your reading to people nearby, those who were directly involved, news articles or your friends.