[antoinevg]

Self-compiled Android without Google services is not a bad place to start.

That said, these single-vendor proprietary mobile platforms are all dumpster fires so it may be time to start developing a free software alternative.

[npo9]

We need free hardware before we can build free software.

No one produces an LTE modem with open source firmware.

[antoinevg]

You absolutely do not need free hardware to build free software.

It was decades before the PC's we used to build FreeBSD, GNU, Linux etc. had even a free software BIOS available.

Historically, free hardware availability has followed in the wake of free software.