Voice quality is good enough for me. Better than small companies.
voice quality is related to voice compressed rate. a standard rate
is 64k/second. Small company makes it to 4k or 8k. Big companies
like bell and primus do compression too, but the rate is much lower.
The game is:
telephone company buy, for example, a 64k voice circuit from Bell.
Then it devids it to 8 circuits each of 8 k.
it sells that 1/8 big circuit at 1/2 of bell's price.
hard compression makes Fax impossible and produces echos, noise, intervenes
also, speak slow costs more.
How to test:
try speak fast in both sides, if no intervene or echo, it is ok.