*Not my guide, this was taken from the Xbox 360 version.Credit goes to SuperEboy
Unmissable and obtained through the gradual progression through the story. Chronically comes 3rd in the story, after
Mission details [Systems Jammed] (verbatim from game):
*** Spoiler - click to reveal ***Go to Concorida and locate the source of the jamming signal.
The Meriff wouldn't see you, Roland and Lilith and nothing to do with Vaults, and Moxxi has a surprisingly large brain under all that makeup. She helped you triangulate the location of the jamming signal, and now she's going to show you the back way out of Concordia.
Turn in: Moxxi