ETOPS -- When exactly?

[BrunoF]

Hi,

I would like to know when an aircraft needs to be certified for ETOPS Operations and what are the requirements.

I know that if you fly though the Atlantic/Pacific Ocean your aircraft would have to be certified for sure. (Up to 2 engines). But on a flight thru the Caribean Ocean, let's assume Miami (KMIA) to Aruba (TNCA). Does the airplane, let's say 737-NG, needs to be ETOPS certified?

Thank you,
Bruno Francescoli.