Palm OS Mobipocket I have can't read mobi files. It can read either kind of pdb files.
Convert the mobi to epub, if there isn't an epub version. Check sanity etc on Calibre viewer of epub.
Convert epub to pdb. Note that neither pdb format understands unicode, so “ ” ‘ ’ € £ and more may be a problem. I forget if I nicely solved the issue.
Later windows, Windows CE, phones and PDAs used mobi and prc formats. The Palm TX seems to have been obsolete at launch (Sold 2005 - 2009) as it runs Palm OS Garnet. There may not be a Mobipocket version for that using mobi/prc.
My Palm Z22 was also very obsolete in 2005 when released. It too Runs PalmOS Garnet and the only Mobipocket versions for it use either "ebook" version of pdb (very primative!).
The Palm TX has a better screen:
https://en.wikipedia.org/wiki/Palm_TX
The Palm Z22 was crazy for 2005.
https://en.wikipedia.org/wiki/Z22_(handheld)
Likely a 2001 Nokia can run a Mobipocket that uses mobi/prc. I had the Nokia 9210i in 2001 or 2002. had to give it back in 2004 when I left the company. I don't remember reading ebooks on it, but you could use Word & Excel files!
https://en.wikipedia.org/wiki/Nokia_9210_Communicator
I used to test fax server installs as it could send and receive faxes via GSM to/from landline numbers/fax machines.
Palm TX seems to have used one of the last Intel ARMs. They sold most of the ARM stuff to Marvell. Xscale may or may not have been based on Strong ARM that Intel got from DEC.
Mobipocket was bought by Amazon in 2005.