Some of the "symptoms" posted above are not too clear.
First of all, is the problem one-way, or does one party (at which end?) hear clearly and one does not?
What connections to the internet are being used?
A dial-up line needs to be of good quality (say 36kb/s or better).
If it's DSL/ ADSL, there should be no problem.
If there's a problem with DSL/ADSL or a good dial-up, then suspect your ISP or the "National service". Of course, if you are sharing an internet with neighbours and they are downloading (or uploading) heavily, your quality is going to be all over the place!
As per my post on page one, I suspect there is something very wrong with Orbit Satnet (satellite connection) as it appears to be nowhere near its claimed 128kb/s "uplink", which means I can hear the party at the other end clearly, but they can't hear me! Anyone else using Orbit satellite connection?