I just flew Jet Blue and I asked two different TSA personnel and both said as long as the bike fits through the scanner I am fine bringing it in. I also asked the check-in attendant and she said the same thing. Then at the gate, the Jet Blue lady said you can either gate-check it or bring it in as a carry-on. I don't know if the Brompton can fit inside of the overhead cabinet but this guy was able to do it according to this picture below.

http://www.flickr.com/photos/cleverc...7622596145551/