Comment 55 for bug 253422

I finally found it! My speakers now automatically mute when I plug in the headphones!
I added the following line to the file "/etc/modprobe.d/alsa-base" (without the quotes):

"options snd_hda_intel model=fujitsu-pi2515"

This is supposed to work for every Fujitsu Siemens laptop. If not you can try the following line:

"options snd_hda_intel model=fujitsu"

My computer: Fujitsu-Siemens Amilo Pa1510 (AMD64 processor)
My audio device: ATI Technologies Inc IXP SB4x0 High Definition Audio Controller (Realtek ALC883)

If you have Ubuntu, just install Ubuntu 9.10 Karmic Koala (as soon as it arrives), since this version solves the headphones/speakers issue in total.