There is no technical difference between a voice VLAN and a data VLAN other then the fact that when configured voice travels on one and data on the other.  

If your talking Cisco config commands the voice vlan is a handy feature which allows the voice vlan to be addedd on top of a standard port rather than setting the port as a full trunk..

switchport mode access
switchport access vlan 100
switchport voice vlan 200

Would set the untagged vlan on the port to vlan 100 and add on the voice vlan 200 as tagged packets. As the previous correspondant says there isn't a great difference in data, although voice vlan's often have extra configs to cover QOS etc..
 

the best config for a HP switch running voice and data is

vlan 1
   name "Data_VLAN"
   ip address x.x.x.x x.x.x.x
   qos priority 0
   exit
vlan 2
   name "VOICE"
   ip address x.x.x.x x.x.x.x
   qos priority 6
   exit
qos type-of-service ip-precedence

thanks


 

CCNA,CCNP,CCVP
HP AIS
Full Mitel  

If the switch supports lldp-med and lldp is turned on then adding voice in the voice vlan will allow the phone and the switch to communicate
and the switch will tell the phone to change into the voice vlan.