The main point of this post is to create an easy (for me) to find list of scrum / agile case studies.
And here it is:
http://agilepainrelief.com/notesfromatooluser/2008/11/scrum-case-studies.html
There is one specific entry from British Telcom that is especially interesting for those in the telcom industry
http://www.magneticreason.com/information/articles/agiletrench.html