[Asterisk-Users] Acceptable voice time delay

[Rob Scott]

Around 250ms max. Over that and you will have the walkie-talkie effect
you are experiencing.
So with you 600ms delay you are way over the top.

There is also the delay on the call on the PSTN side you have to take
into account.
For example, I am in Europe and making a call to the UK via Voipjet is
usually OK.
But making a call to Romania is a lottery. Sometimes it is great,
sometimes the delay is huge.
And that has nothing to do with the internet delay which is more or less
constant at around 180ms for me.

But with 600ms, which is over half a second, you have problems.