Finally there is an application which allows you to use the flash of your Nokia 5800 Xpress Music as a torch. This freeware application is also already signed. Currently PhoneTorch just runs on the 5800 but the developer tries to write a S60 3rd Edition Feature Pack 2 version.
PhoneTorch is still under development and usage is at your own risk. Intensive use of the camera flashlight might lead to device damage.