Recently off the Horizon, and purchased premium.
While IN MY CABIN (Deck 7 Ocean Suite), reliably had speeds of 300Mbs while in port, and 50-60Mbs while at sea. However, while at sea the latency was extremely high (as can be expected) causing some operations to time out occasionally and requiring several reloads/refreshes.
WiFi calling SMS/MMS was not supported. If on Android, ensure you have RCS enabled in messages and texting to other Android users will work as long as they also have RCS enabled.
We were pleasantly surprised with the number of streaming services that worked. I tried the following:
Netflix (Does not go out over the internet gateway, ship has a local caching server)
Prime Video (UI via satellite gateway, some content appeared to be coming from a local cache)
Hulu (Did NOT work, hard block)
ESPN (Did NOT work, hard block)
Disney+ (Did NOT work, region blocked)
Pluto (Did NOT work, hard block)
AppleTV (Did NOT work, hard block)
Paramount+ (Entirely via satellite, Latency was a major issue I was rarely able to overcome)
SlingTV (Entirely via satellite as expected. Latency was an issue requiring many attempts to get a stream, but once started worked great)
Sirius/XM (Entirely via satellite as expected, worked flawlessly)
OUTSIDE the cabin, while out and about, it performed rather poorly, with speeds of about 5Mbs. In some of the most guest populated areas, even the Hub app would not work properly.