Can you give me an overview of how voice over WLAN works?

If you notice, I always refer to "VoWLAN" as "wireless VoIP". That is because that's all it is! Basically, a model called the Open Systems Interconnection or OSI model governs all networking. The model defines different layers of networking and sets them up such that you can use different technologies at each layer without worrying about the layer above or below the one you are addressing (more info here http://cne.gmu.edu/modules/network/osi.html).

Now, IP is a "Layer 3" technology and is used to encapsulate digital voice so that it can be transported. "Wireless" or, in the case of VoWLAN, "802.11," is a "Layer 2" technology. Therefore VoWLAN is simply Voice over IP over 802.11 wireless Ethernet. When people refer to regular VoIP it can be running over Ethernet, SONET, Token Ring, T-1s, whatever. The underlying transport doesn't matter and that's the simplistic elegance of the OSI model.

Net-net: VoWLAN is simply VoIP running on a wireless local area network. Someone slapped the acronym together because that is the nature of High-Tech – everything needs a catchy acronym.