First, do not panic and do not try to force the door. A credit card might work in the movies, but on a real Manhattan deadbolt it will only damage the card and possibly the door. Check the obvious: an unlocked window you can safely reach, a spare key with a neighbor or doorman, or a building super who can help.
If no spare is available, call a local locksmith — not a distant call center. A shop based in your part of the city reaches you faster and knows the building stock. Have a photo ID ready; any legitimate locksmith verifies you are authorized to enter before opening anything.
When the technician arrives, expect non-destructive entry first: professional picking and bypass tools that leave your lock and door intact. Drilling is a last resort and should always be discussed with you before it happens. After entry, consider rekeying if your keys were lost — especially if the lost set had your address on it.