This just seems like such a dated and irrelevant stand for Delta to take. Cellphones are here to stay. We live in crowded spaces and it's time for everyone to simply get used to the sound of other humans.
I have no idea why everyone places value on public silence. Is this a holdover cultural strain from the 19th century? Silence is so cheap and so easy to obtain. (And who wants to be the one to make rules which essentially say "shhhh!")