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.
Mobile app developers, if you haven't read Zen of Palm, I highly recommend this piece of art. You can download the PDF for free. Nothing beats Palm for its simplicity, responsiveness, and (perhaps subjectively) ease of use, even to this day.
I wrote a series of blog posts about it nearly two decades ago, and later translated some parts into English: https://dingyu.me/blog/zen-of-palm-1-preface
EDIT: Disregard, found it: https://archive.org/details/zen-of-palm
Developing for is was a fun challenge. I had a device that had 4MB of memory total. This was RAM, Data, and application space. I created an "app" that had plugins. When you ran the HotSync is asked which plugins you wanted to "install", then based on which ones were installed it copied over the data you needed.
I loved the documentation. It might be the only SDK documentation I read with joy. It just clicked with me.
Gremlins. I liked this program as well. I don't recall if it was a simulator only or if it ran across on device. You could tell it to just wreck havoc on your app. I would set it up to run over the evening or weekend and I would just fix any bugs that occurred during that time. It would click every button, add weird text to all input boxes, just smash everything. It found many issues for me. When I came back over the weekend and there were no issues, I shipped my app. I still had users running it up until 2010.
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.
"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.