On Issue Tracking Systems

I have found Issue Tracking Systems to be much more convenient than email in many tasks.
In any organization having an Issue Tracking System is a must as it keeps clear what task should be done by what department and who is the person assigned the task.
The problem is that as currently business work they never show the issue tracking system to an outsider (aka client) but instead the client must always communicate with the call center. An issue tracking system should be open to outside client for maximum effectiveness.

Any company or project should always use an issue tracking system.

My favorite issue tracker is Bugzilla, but I would change the comments list with a wiki entry and associated discussion (like Wikipedia has) for every issue.

Popularity of Issue Tracking Systems among developers