Seen them run a tube out of the overhead and duct tape it to wall. FA thread is probably the place for more in-flight info.

A while back I was standing first in line on red carpet (yea,yea,yea with both bluetooth), GA calls a young guy over who did not speak very good English. Trys to tell him to go to counter to pay some charge. After he left she tells me that he ordered O2 but hadn't paid for it. Says with a wink "yea, people try to get by with that all the time".