I have no problems with VoIP compression -- it's actually better (more bits) than the compression with POTS (56Kbps in Can/USA, 64kbps in EU). And mostly the same for GSM (mobile) voice.
But latency. Oh, latency. Killer.
I have to say that the cellular network audio quality here has been worsening significantly over the years. Signal tends to be weak, so conversations are way too frequently disappointing (broken, with "statics", dropped). In addition to latency, of course.
I wonder how much of this is partly caused by Smartphones being generally weaker in reception due to their embedded antennas? Do you think this makes sense?