When I try to have KDE start a SIP softphone via a xdg-open call the following error msg shows up:

Could not start process Unable to create io-slave:
klauncher said: Unknown protocol 'sip'.

But I can't figure out the proper way to configure KDE to fire up my SIP application of choice. I'd appreciate being pointed in the right direction, or even given the right syntax?

This can be done through the *.desktop file of the application in question, assuming it has the right elements present in it.
You just need to associate it with the right mimetype - KMail uses this for instance:

Code: Select all

MimeType=x-scheme-handler/mailto;

Hope that helps.