I'll edit this a little better later:
Maddison received postcard postmarked Fort Worth, with the image of Dallas on the front. She, Adam, and Maddison's friend drove to a Starbucks in Dallas with the postcard, then Skunkwaffle decoded the message using T9. (As Clemetine put it, "yep...skunk put the stink down on that code.") It translated to, "Trinity hall pub."
This link shows the path the team took from Starbucks to the pub.
lg15panda linked to the chapter and page of the quote from "The Old Curiosity Shop" that T wrote on the postcard; find it
here.
ApotheosisAZ located an image of the interior of the pub showing a bookcase, and QtheC called to verify.
BrightSilence was in direct phone contact with Maddison, and Skunkwaffle was in direct phone contact with Roytheboy.
Bright's phone conversation recordings are available
here.

