Lean processing was initially developed by Toyota. The innovation was to work in terms of flow rather than focussing on speed of production. This has been covered in many books:
The one that I am reading now is Freedom From Command and Control
This is an attempt to translate the Toyota process for service organisations, and in particular customer service.
The overall idea is to find and eliminate waste. Those best placed to detect the waste are those doing the work.
A starting point would be categorising calls into value vs failure management. Failure management results in finding things that should not happen. If these can be prevented then the volume of wasted repeat calls will decrease.
Developer Rants 