That would have been a catastrophe -PHEW!

for the flight numbers (3828 and 1328)...maybe someone should think twice about having two such similar call signs also be so close in time of departure.

Smart pilots also readback clearances to insure such mistakes don't happen. The call signs are based on the airlines internally generated flight numbers.

It still seems to me that the Delta pilot misheard...maybe a moment's inattention, maybe the transmission was partly stepped on. Still think the flight numbers should be changed.

At someplace like O'Hare, Atlanta, or DFW it would not be uncommon at all for many planes to have even more similar callsigns throughout the course of a day.

Most (if not all) major airlines have internal policies that require pilots to readback instructions. I'm not sure what was going on with the United flight, but it sounds as if they just blew it and fortunately ATC caught their mistake.

but "similar callsigns throughout the course of a day" is not the same thing as similar callsigns for flights that are departing--in this case literally!--simultaneously. It amounts to a quibble, in the grand scheme of things, but maybe it contributed to this near disaster.

For one thing, the actual flight numbers are not assigned by the FAA, but rather by the airlines themselves. There's also no way to accurately predict that far in advance when two aircraft from two different airlines would be simultaneously departing. Aircraft simply file proposed times for takeoff, but the actual times can and do vary by as much as hours on either side.