Sony PC Companion is a set of tools and applications you can use when you connect your device to a computer. Sony PC Companion contains Xperia Transfer, a tool for moving content from an iPhone to your new Xperia device. It also offers device software updates, contacts and calendar management, and a backup and restore feature for your phone content (availability of applications depends on your phone and operator).
You can also transfer and organize your media content using Media Go. Over time, more applications can be added and downloaded when made available by Sony or your operator.
Note: Sony Mobile recently launched “Xperia Companion”, which is a new program for your PC to help manage your Sony Xperia device. If you are still running Windows XP you will need to keep using PC Companion.