Update Nov 11, 2009 :

Do not follow this post and please update your installed package using your favorite package manager such Synaptic or apt-get or whatever and your Broadcom BCM4312 will working properly :

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install linux-backports-modules-karmic

If your Broadcom wireless BCM4312 did not working after upgrading your packages because of you did what this post say, please roll back your changes :

#unblacklist ssb module :
sudo echo "" >> /etc/modprobe.d/blacklist-ssb.conf
#unblacklist wl module :
sudo echo "" >> /etc/modprobe.d/blacklist-wl.conf
#restarting your system :
sudo reboot

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For a week I can’t use my wireless. This problem makes me installing fresh Ubuntu Karmic Koala in my lapie for 3 times, sadly .
First of all, if your system same as my own, just try this trick. But if different, hmm, try with google .
I found this trick from Ubuntu Forum posted by chenxiaolong, thanks chenx, you save my lapie.
So, open your terminal, and check your wireless first :

lspci | grep Broadcom
03:00.0 Network controller: Broadcom Corporation BCM4312 802.11b/g (rev 01)

If your wireless looks like that, let’s continue :

#install linux backport :
sudo apt-get install linux-backports-modules-karmic
#blacklist ssb module :
sudo echo "blacklist ssb" | sudo tee -a /etc/modprobe.d/blacklist-ssb.conf
#blacklist wl module :
sudo echo "blacklist wl" | sudo tee -a /etc/modprobe.d/blacklist-wl.conf
#restarting your system :
sudo reboot

That’s all, after restarting, enjoy your wireless
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