Originally Posted by JS
For confirmed tickets, the answer to all of your questions is no. You absolutely cannot use a co-terminal's fare. Fares may only be used to ticket flights from the airport for which it is published.
It is possible to stand by from a co-terminal airport, but it's hit-or-miss.
This past summer, I was flying ORD-LGA on UA and asked about standing by on a ORD-EWR flight. When they said no, I asked aren't these co-terminals, and was told that since BK not really and that I'd have to pay the change fee to do it.