Comment 17 for bug 732677

If you read the previous comments carefully you will find this potential workaround. I can't confirm it works but Broadcom reckon it's a common issue:

[from http://www.broadcom.com/docs/linux_sta/README.txt]
* If the wl driver loads but doesn't seem to do anything:
  the ssb module may be the cause. Sometimes blacklisting ssb may not
  be enough to prevent it from loading and it loads anyway. (This is mostly
  seen on Ubuntu/Debian systems).

  Check to see if ssb, wl or b43 is loaded:
  # lsmod | grep "b43\|ssb\|wl"

  If any of these are installed, remove them:
  # rmmod b43
  # rmmod ssb
  # rmmod wl

  Back up the current boot ramfs and generate a new one.
  # cp /boot/initrd.img-`uname -r` somewheresafe
  # update-initramfs -u
  # reboot