Heh. The N900 was an amazing device and I cherish the time I had with it.
However, it's also a painful memory, because I managed to brick the device after spending possibly hundreds of hours customizing it.
The first thing I did was let the micro USB port come loose--a common problem with the device, which seemed to happen to many over time. I remember still being able to charge it somehow (maybe I bought an external charger?). However, the nail in the coffin was when I was cleaning up some "unnecessary" cruft in the init directory, ostensibly to make the thing boot faster.
What I discovered instead was that there was a watchdog that monitored for the existence of crucial files, and, failing to find them, the phone would reboot itself. So my glorious N900 was caught in a bootloop, and moreover without a functioning USB port to re-flash the operating system.
Behind the battery, there are CPU pins that are directly exposed through a grid of copper pads. I made an attempt at wiring up a makeshift soldering job directly to the pins corresponding to a USB port, but failed to confidently pull off the dexterity to work with the small surface, as well as the care to do so without heating things up too much.
Of course I believe there existed a development device with pins that directly clamped onto the pads, but if such a thing was publicly available it was probably hard to come by at affordable prices.
I later tried to realize a similar experience to the N900 on Android using stuff like tmux and F-Droid. However, I have no good memories of any phone after my Nokia, and pretty much don't like phones at all at this point, and now just use my iPhone SE as a glorified flip phone with maps and a web browser.