A thread over on FlyerTalk says these United aircraft have channel 9 in the seatback entertainment:
The last four times I've asked the FA's to ask the pilots to turn on Ch. 9, the FA's have gone away to ask and then reported back to me that the pilots said 'no'.
Honestly, Channel 9 won't be terribly relevant for much longer outside of the terminal area anyway.
Tower and TRACON will continue to rely on voice comms (although Clearance Delivery has been automated at most major airports for years), but Enroute is currently phasing in datacomm using CPDLC. Indy and Kansas City Centers have been in testing for a few months now, and most centers will have datacomm fully operational by the spring or summer.
Initially, it just means that things like frequency changes and some basic control instructions (like altitude changes, descend via clearances, speed changes for in-trail spacing, etc.) will be via text instead of voice comms, but eventually most communications between controllers and pilots during the enroute phase will be automated. It won't be a replacement for voice comms, but it will make many frequencies pretty quiet for most of the time. Maybe Channel 9 will still be nice for taxi and takeoff/landing, but outside of that, it will get increasingly boring in the coming years.