This was achieved by porting the FreeBSD WiFi stack utilising Haiku's FreeBSD Compatibility Layer, which means he could use the FreeBSD Atheros driver with only minor code changes. "I had to move some interrupt handler code into driver-specific glue code," Günther writes. It's got some severe limitations though; it can only connect to unprotected open networks, and there's no configuration mechanism yet.
The code is actually already in the SVN repository [not in the official Haiku one, though], but it's for the brave among us only, and obviously only works for Atheros chipsets supported by the FreeBSD driver. Günther compiled the code using a GCC2 build environment and the latest build he tested his code on is Haiku rev. 31286.
Haiku is really shaping up quite nicely, and I hope they can get the alpha release out the door before Christmas. Exciting times!