None. The sad, infuriating truth is that the makers and devs are a lot like this comments section: focusing on how good of a computer it is (or what apps it has).
You do a little digging and beneath all the hype there is a line buried in every review, so as not to raise suspicions, that says something like “now the call quality isn’t perfect, but…” and what they mean is “it will sound like your friends are playing a full concert on a kazoo trying to talk to you.”
Time and time again. Every linux-based, privacy-respecting, freedom-loving phone team out there seems to have conveniently neglected to make the phone good at being a phone.