Rail is a frequently used slang term for a dose of cocaine. Many drug-addled callers will simply regale Tom with stories of their drug-soaked pasts and present, while some will actually do a rail during the call -- and then often deny it.
A good example of this phenomenon occurred during the 4/4/06 call from Larry Smirthwaite. Larry paused, returned to the phone with extremely quickened speech patterns ("Isounddifferent?"), and disputed Tom's charge that he has just done a rail. He claimed it was simply a few sips of Mountain Dew. He also noted that he couldn't wait to start dancing.