I have some requests which i believe would improve the desktop UI.
With an extra option to enable/disable such behavior, when an incoming call is received, instead of showing the main window, a smaller popup window near the tray could be shown, with some basic buttons in it (answer, drop, forward to voicemail, forward to another number, etc). When the call is dropped (either by the user or by the remote caller), the popup would automatically close.
The tray icon's context menu is rather poor. It would be great to be able to define some favorite numbers from the address book, which would be added to an extra submenu (Favorites) of the tray icon context menu. That way, the user could click on any of them and a call would be immediately placed.