United Airlines and now American Airlines have decided that for some travelers, bicycles are essential equipment, and are now recognizing bicycles (and other large pieces of recreation equipment like surfboards) as "standard" checked luggage. You'll still have to pay a baggage fee of $30, but that is down rather significantly from the "oversized" fee of $50 and more that they had been charging.
Of course, you'll still have to box the bike, and if it exceeds weight limits, you will be charged for the excess weight.
here's a good article from about a week ago with some of the same information. They have the police change at American but not United.
It also talks about the pros and cons of hard vs. soft bike bags.