A user on the XDA-Developers forums has written a tool using .Net that allows users to “back up” the contents of their Windows Phone’s memory (including files placed via the mass-storage enabler).
“This APP is a wrapper around a tool microsoft produced to perform updates to your phone via command line. Specifically the executeable “updatewp.exe” that comes from the Windows Phone Support Tools. updatewp.exe is meant to update your phone with PKS files theoretically obtained from the device manufacturer. It will also do other things including a command line restore of a backup.
What happens is the phone performs the backup first, once it completes the process the code terminates updatewp.exe before it goes further. In theory if you are using an update not compatible for your phone it would actually just say that and quit. However terminating the updater keeps it from ever getting that far.”
In short, this tool uses the executable to back up your WP7 device, although it was originally intended to back the device up, and then perform a software upgrade. The tool uses launches updatewp.exe with the intent of updating the device using the update packages from an HTC HD2, triggering a backup of the device to a specified location, and then terminating updatewp.exe before the actual software upgrade takes place.
For restoration, just go to Zune software (with the phone plugged in), go to Settings, then to Device (or Phone), and click Update. Text at the bottom of the window should appear, indicating the path/file used to perform the restore.
More Info: XDA-Developers