A vLan is simply a virtual lan that is separate from other vlans on your network. If you separate your voice devices from standard data devices using a vlan, those voice devices do not have to contend directly with all the broadcasts and other traffic from data devices. +1 on no competition.
Another advantage is that you can mark an entire vlan as priority (QoS). Think of that! You don'thave to mark ports for QoS, instead you just mark a vLan...much simpler.
Here's a many part article on vLAN's and why they are important. I'm not saying it's easy to do...it's just something that you might think about...having a data vlan and a voice vlan is far less problems than the 30 I have at work! www.formortals.com/an-introduction-to-vlan-trunking/