LLZ:
Never knew DL to offer ATC or tower communications as part of their IFE during the nearly five years I worked for them (1978-83) and, later, as a revenue passenger on their flights. AA definitely had the cockpit video cameras (and possibly tower communications on audio) on their DC-10s; perhaps on other aircraft as well. The system was activated for take-offs and landings so passengers could watch the cockpit crew and see the runway ahead. Sadly, after the crash of one of their DC-10s at ORD, in May of 1979, the cameras were removed.
FCfree:
To my knowledge, UA offers inflight audio on every aircraft in their fleet except the 737-200s (and I hope there are few of these remaining!). I have always regarded UA as a leader in inflight audio - not just because of "Channel 9" but because of the superior audio quality offered, especially on their CD-equipped aircraft. Audio quality on UA's 777s, A319s and A320s is absolutely superb for an IFE system. And, if you bring along a good pair of noise-canceling headphones, you really have it made! UA's 747-400s also have excellent CD audio, at least in "United Business" with the noise-canceling headphones they provide.
If memory serves, NW offered audio on their A320s when I flew them in 1991 but perhaps they no longer do. (?) Can't say about other operators of the A320.
(edited for clarity)
[This message has been edited by bbinchi (edited 04-05-2001).]