Hi Kurun,
Thank you for your fast response.
I have a 4Mb ADSL connection, the speed tests which I periodically repeat do give acceptable results (
MySpeed VoIP connection test, VoIP test, test VoIP performance, test VoIP quality VOIP test reports radio quality). Although my ISP's QoS (Quality of Service) is not shining, I have had high quality communication with an Nokia E90 (which I told in my first post) with the same connection, which forces me for a finetuning solution research.