Today, VoIP over LAN can be managed much more effectively. First, QoS is automatic. Second, wired and wireless LANs are engineered with so much bandwidth that session traffic can happily coexist without even approaching saturation.
But, if some sort of traffic management is needed, it is applied automatically through real-time packet inspection. Most network devices — even low-end ones — are powerful enough and smart enough to diagnose the applications funneling through them. Once VoIP over LAN traffic is detected, the devices place that traffic in high-priority queues. In the event congestion occurs, the device allocates additional bandwidth to resolve potential quality issues.
To ensure good performance, check the configuration settings for each device across your VoIP over LAN deployment. Many will likely default to providing QoS. With others, you may need to enable QoS options, but those controls should be applied automatically from that point on. It is rare to find any device requiring manual queue configuration, though some may offer that option for more advanced needs.
It sounds paradoxical to say, but even if QoS remains as important as ever for VoIP, from an implementation point of view, you can usually just forget about it. Your network devices will take care of it for you.