About VLAN 0

I have read all the comments posted in this article. This is really an interesting topic "VLAN0". I have also asked some of my friends who are network administrator in different compnies, but they alos failed to relpy the exact query.
I have received the all the answers with if's and but's, no straight forward reply.

I have a query regarding "VLAN 0". What is this VLAN 0 and is that configurable in a swich? Please through some light on this

Actually it's quite simple. Voice traffic must have a CoS applied to it to give priority over data, the layer 2 CoS is 802.1p which resides WITHIN the 802.1q header. Some devices are configured WITHOUT 802.1q frame tagging for vlans, however without dot1q, you cannot have dot1p, so therefore if you configure access ports where the phone(voice) and pc(data) reside on the same vlan, with no explicit configuration for a voice vlan, the phone will tag the voice frame with dot1q and insert a vlan of zero telling the switch they are only using dot1p and that the frame belongs to the native vlan