With all mobile ecosystems closing down, I am considering switching to dumb phone. It will be used for calls and SMS only. For all my personal computing and hobby projects I would like to have some additional device that runs open source software, and does not prevent me from building and running custom applications. It would be amazing to have some device similar to classig Palm Pilot, "handheld PDA". Maybe even with stylus, 4"-5" touchscreen that easily fits anywhere. Are there any similar devices available? Tablets are way too large and are using same closed mobile ecosystems.