Just flew DSM-DEN and couldn't get onto internet with my annual subscription, on my laptop. Subscriber sign-in took me to united.com, I put in my credentials, and then it asked me for the 6-digit code it just sent as text to my phone ... which of course I couldn't access at 30,000 feet. Onboard wifi entertainment worked fine. Flight attendant suggested chat (had no idea that was option inflight) and chat guy had no idea what the problem could be but did send me an access code for "free" session for that flight - which did work.

Now at Club in DEN, called Mileage Plus Web support and the nice guy and everyone he asked had not heard of this problem. He had me sign into my UA.com and I got the same SMS code request (yesterday I still had the questions). He said "that is something IT is working on but I didn't think it was live yet." He suggested I stay logged into my UA account on my laptop and see if I can get on on my next flight here shortly.