@postmarketOS Actually, which project could be considered the first one? 🤔 Let's ignore PDAs as their history is longer.
The earliest one I'm personally aware of is @LaF0rge's OpenEZX from 2005, targeting Motorola's Linux phones.
https://web.archive.org/web/20051029042914/http://www.openezx.org/
@dos @postmarketOS yes I presume OpenEZX might have been the first attempt at open source software for the application processor of a smartphone. At least I didnt know any other such project back then. It sadly never went very far, as several key contributors including I got "distracted" with doing #openmoko - but that was also a good thing, of course