Broadcom has declined so far to provide any non-licensed access to its Wi-Fi chips: A project that has been working to reverse engineer access using legal means has released its first working drivers for Broadcom 4300 series chips. The project requires the use of the SoftMAC software as well to compile working drivers within Linux. The first successful use was documented in email Dec. 4 to the developer's mailing sent from a PowerBook running Linux with the project's drivers installed.
Atheros has allowed a third party to create a layer between the low-level functions of its chips and high-level drivers. The madwifi Hardware Abstraction Layer (HAL) prevents developers from having access to most of the radio functionality, which would might allow use of frequencies that aren't legal in particular countries, use of encodings that aren't allowed, and other regulatory problems.
The Economist magazine ran an article early this year critiquing the timidity of Atheros and Broadcom, noting that "if the firms are really worried, they could release most of the interface, keeping back those features that are legally sensitive." Neither Atheros nor Broadcom speak much publicly about this matter. [Link via Jim Thompson]