Connecting between airports can get expensive quickly. I always assumed that you had to pay for your own ground transportation if you booked a flight that required an airport transfer. While researching this issue for a friend a few days ago, I found that this is not the case on Delta for some international itineraries connecting in New York City.
According to Delta’s contract of carriage, rule 30, Delta will provide a ground transfer between Newark International Airport (EWR) or LaGuardia Airport (LGA) and John F. Kennedy International Airport (JFK) if you are making a same-day connection to or from a trans-Atlantic flight. Both flights must be issued on the same ticket and the ticket must not be a “free” ticket. (Conceivably this means that people traveling on frequent-flyer tickets are out of luck.)
While Delta makes little effort to promote this service, a few FlyerTalkers have figured out how this works: The baggage service office will issue a voucher and help you to arrange your ground transportation upon arrival. Alternatively, you may submit receipts for reimbursement.