04-08-2010 03:31 PM - edited 04-08-2010 03:34 PM
This was a feature temporarily added to BlackBerry OS and then removed.
Normal behaviour for Alt+Backspace is to delete one character. However, some programmer at RIM thought it would be useful to delete the whole SMS message with this shortcut. There were many complaints, and this shortcut was removed in the newer BlackBerry OS.
Go to your carrier's website and download the latest BlackBerry OS, to remove this annoying feature (which sorta killed me too).
If your carrier does not provide the latest, there are undocumented (RIM-unapproved) hacks to install a different carrier's newer BlackBerry Handheld Device Software to your own BlackBerry. They are relatively simple and low risk, often a single added step (deleting a vendor.xml file) to the regular procedure of installing a new BlackBerry OS. A few others, has resorted, to the installation of beta newer OS 5, to resolve this problem. (RIM disapproves of this, as these are generally illegal leaks)
Hopefully I'm worth a kudo or two for saving your BlackBerry insanity!