I thought I'd mention that I notice more jitter on my VM 50M service than on my O2 16/2 service.
From
http://myvoipspeed.visualware.com/ - London server:
VM:
VoIP test statistics
--------------------
Jitter: you --> server: 20.9 ms
Jitter: server --> you: 18.1 ms
Packet loss: you --> server: 0.0 %
Packet loss: server --> you: 0.6 %
Packet discards: 2.8 %
Packets out of order: 0.0 %
Estimated MOS score: 3.6
O2:
VoIP test statistics
--------------------
Jitter: you --> server: 3.1 ms
Jitter: server --> you: 10.6 ms
Packet loss: you --> server: 0.0 %
Packet loss: server --> you: 0.0 %
Packet discards: 0.6 %
Packets out of order: 0.0 %
Estimated MOS score: 3.9