If you are getting these kind of errors when you try to install java on debian under a virtual machine, then you perhaps need to increase the available memory.
Yesterday I had some problems with the VOIP connection. I heard my party very well but he could barely hear me.
Normal run of mtr to the other host showed no packet loss but I was able to pinpoint the packet loss to the other party with
mtr -n -s 200 -i 0.02 [ip-address]
(you need to be root)
which sends 50 packets/seconds 200 bytes/packet which pretty much emulates the rtp stream.