No subscriptions! Either the applications were free or it's a one-off fee/shareware kind of thing.
And it's ofcourse nostalgia, I made my first game for Palm OS over 20 years ago, it was nice to revisit it and get familiarized again with how the whole build system worked.
"I have fond memories of some z-machine interpreter on the Palm that I found easier to play with than anything on my desktop computer. There were lots of shortcut buttons and thanks to the stylus it was still easy to use those (vs a touchscreen using ony fingers where you need huge buttons to hit). You could also tap any word in the output to bring up a context menu of actions (e.g. to examine or pick up objects mentioned in room descriptions) and that list of actions was a combination of a configurable global list and a game-specific list you could add actions to. Could play through entire games and barely ever have to type anything. Had a folding keyboard, but no memory of using that for interactive fiction."
From looking at my old hoarded palm files I think that the interpreter was PalmPilotFrotz, still available on the if-archive: https://ifarchive.org/indexes/if-archive/infocom/interpreter...
On smartphones, FDroid for Android had the Anysoft keyboard with a swipe option, it works great, much better than typing. There's also some grafitti 'keyboard' input at FDroid, but I prefer the swiping one as it's far superior.
On the old T9 phones, OFC a Frotz port exists for J2ME, but I didn't try it.
I had a foldable one with (almost?) full-sized keys that I really enjoyed using. It connected via infrared, which was a bit strange but made it compatible with different generations of device connectors.