This, exactly. I have two ancient Nokia N900s that came out in 2009, runs a Debian variant natively and there's the Maemo Leste project that brings mainline Linux to the device (amazing!). However, is already useless as a phone in the USA. I also hear rumors European carriers will shutter their 3G networks soon; which is a shame. The hardware, while old and slow due to memory constraints, still works. I guess I should relegate it to being a small multimedia server in my apartment.

The planned obsolescence of today's mobile phones makes me sad.