So as a United flier(haven’t flown for two months, though), I know that they provide the following free:

• a selection of locally hosted movies and TV shows
• RCS, iMessage
• Internet messaging services like meta messenger and snapchat(I can’t speak on more niche messengers like Jami or any forms of XMPP

You have to pay extra(or sign in with t-mobile) to get in flight internet access.

I hope that this means that you’ll get unrestricted internet access for free, instead of only a few apps and services.