Why use a single-channel WLAN?
Blanket your building with one-channel of Wi-Fi.
Putting every access point in an enterprise WLAN on the same radio channel sounds dumb. But a growing number of vendors claim it does away with co-channel interference, and makes a WLAN that can handle voice without breaking a sweat.
Most WLAN systems include planning systems dedicated to preventing any adjacent APs ever having the same radio channel - which can be an elaborate dance. In the case of 2.4GHz WLANs, using 802.11b or 802.11g, there are only three channels that don't overlap.
Also, when a client device moves from one access point to another, it must hand-off between the two, which can cause delays that scupper decent voice transmission.
Single-channel WLANs throw that out, by putting every access point on the same channel, so a single channel "blanket" covers the building and the client never roams: its connection remains continuous, while the WLAN system sorts out flows to the different access points it uses.
There's a technological price to pay of course, mainly in sorting out traffic flows at the switch, and making sure that airspace is re-used where possible, by clients out of each other's range. While you may fear lower capacity, it is possible to add other channels, each with their own blanket across the building.
This Meru white paper dates from last year. To be honest, it's basically a product pitch, but it does contain a cogent description of the single-channel approach and why it might be better for voice. Well worth dissecting, to keep up with what could be a crucial argument for future Wi-Fi deployments.