I don't think this is true.
> If you have specified that you don't want an assigned (preferred) LD
> carrier, then a LD call DIALED "by accident" would not complete.
> Random carrier assignments are only made for those customers who state
> that they DO want LD service but don't have a preference for which
> carrier is used. This usually only happens when a new line is
> activated (installed, connected, turned on ... whatever).
> If you have specific information about a LEC that will do what you
> claim, please provide the details.
I suspect you are correct, but I have insufficient data to tell, conclusively, from my experience.
Brief summary follows. Location, SBC, former Ameritech, specifically Chicago. Incident involved intrastate local toll rather than interstate LD. I had switched interstate LD carriers, and during the transaction, without my knowledge, local toll carrier on one of my two lines apparently was listed as unassigned, as you speculate. I rarely use that line for outbound, but one month I had two local toll calls. Both were assigned (randomly?) to Sprint, which charged me $1.19 a minute (!) for a call from Chicago to Wilmette, a Chicago suburb.
After a bit of argument, it was agreed that SBC made the error, and charges were reversed.