I've the same bug in my Panasonic CF-W5 laptop that has SIgmatTel STAC9200, i.e., no sound from internal speakers, but headphones work fine.
$ cat /proc/asound/card0/codec#* | grep Codec
Codec: SigmaTel STAC9200
Codec: Conexant ID 2bfa
I don't have sl-modem-daemon package installed. I installed linux-backports-modules-alsa-karmic-generic and rebooted, but no difference.
If you need the information, I can also do "apport-collect -p alsa-base 471208".