When I worked at a call centre (Help desk for a major computer manufacturer's home computer line) we were actually told we were required to give last name if pressed, and we all heard horror stories, I even had customers yell at me that they were going to find me and shoot me. Which considering the fact that I lived in a different country than the client I was confident that if they could find me, the worst they could do is stab me. When I was there, we did receive a bomb scare from a disgruntled customer (although I personally think it was a disgruntled employee). And they took it seriously, the police went through every desk, every room, etc. The call centre was down for an hour.
I can see collections not releasing names, I suppose it really depends on whether it's an inbound or outbound call centre.