Originally Posted by
Totoro
For purposes of standby, EWR and LGA are not co-terminal airports, and you therefore cannot switch. LGA and JFK are considered co-terminal airports. The only time CO considers EWR and LGA co-terminal airports is at their convenience (e.g. MX problem cancels your LGA flight, and they have seats to EWR).
While this may be official policy, it doesn't mean that it can't be done. My co-worker got on the EWR flight yesterday instead of the JFK one (and I know that the fares were very different for EWR/JFK on our route) thanks to some help in the PC. He was the last standby boarded on a flight that initially was oversold, so not too bad overall.