In helping a new user get comfortable with their N900, I found that one of their biggest complaints involved not having a dedicated hardware "end call" button to ensure that no active call existed. Sadly shortcutd doesn't quite suffice, since only the half-press of the camera button can have a shortcut; a full press of the camera button with the lens cap closed will always just bring up the camera app and say "Open lens cover". However, I did manage to put an "End call" option in the power-button menu, and that menu works from anywhere on the phone.

I've attached a file endcall.xml.txt. Rename this file to endcall.xml, and put it in /etc/systemui/ ; if you have ssh properly configured, you can just run:
You could also use "localhost" from your n900.

After copying the file, you need to restart systemui to make it re-read its configuration files. You can either reboot your phone, or run "killall systemui" via xterm or SSH.

Then, when on a call, you can press the power button and you will have an option "End call", complete with the appropriate icon:





If people find this useful, I may package it up in a Debian package and upload it to extras.