The only way to have "codesharing" without different flight numbers, operating carriers, and so forth, is for the airlines in question to merge.
The fact that Piedmont Airlines doesn't publish two different flight numbers (just the US one) is irrelevant. Ever try to buy a ticket directly from Piedmont?
Give me a row of monitors full of flight numbers for three aircraft any day over a massive merger of airlines (never mind that the feds wouldn't allow it).
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"It's as easy as 1, 2, C" -- Kelly, Married With Children
[This message has been edited by JS (edited Dec 02, 2003).]