ETOPS is a very maintenance centered program. An ETOPS flight is in many ways an ordinary flight with some additional flight planning rules. But the maintenance program is the key.
An airplane must be maintained under an ETOPS program to ensure certain minimum levels of system reliability and proper airplane configuration. Depending on the airplane some parts may have to be swapped out to meet these reliability standards and to conform to an approved configuration. If an A321 meets the standards, then there is no reason that it could not be used in ETOPS. Some 737NG and MD80 are approved for ETOPS today.
If you really want to know the specifics, you should go to the FAA website and pull up the Advisory Circular on ETOPS.
Military airplanes use
UHF. DL757md is correct about
HF.
[Edited 2004-10-17 11:55:20]
[Edited 2004-10-17 11:57:48]