Software
The PinePhone will automatically boot from microSD if a bootable card is inserted. Although it is technically possible to use any ARM distribution (because the PinePhone uses the mainline kernel), there are a few that are designed specifically for mobile use on devices like the PinePhone.
Software releases
The Releases page has a complete list of currently supported phone-optimized Operating System images that work with the PinePhone as well as other related software information. As soon as more patches get mainlined and distributions ship with the updated kernel, they will also be able to run unmodified on the device. To update any installed operating system please see Update instructions.