Hello,
I too have same problem as above. No sound on being called, only lights and vibration. I had nothing extra installed, I don't use the headphone.
I've tried all above suggestions, without succes.

On cp /opt/maemo/usr/lib/libFLAC.so.8.2.0 /usr/lib/libFLAC.so.8.2.0 I get error message cp: cannot stat ' /opt/maemo/usr/lib/libFLAC.so.8.2.0': No such file or directory

on start pulseaudio it returns -sh: start: not found

I went so far to flashing twice, still no sound on being called. Having flashed, there is no extra software, still the speaker gives muted sign.
Please help, for the phone is useless this way.

Do you have a sound at all if the phone boots with the nokia shaking hands intro?

Yes, all other sounds work.
I flashed the rootfs but that didn't make a difference. I think I will flash emmc too. Thats all thats left over to do, I guess. But I do agree with the others that I too wan't to know what caused it.

This post sums up my experience with this issue http://talk.maemo.org/showpost.php?p=882093&postcount=4 May be it helps you, too.

Since i was experiencing the same issue:
" voice-hw-sink-input.c: Master sink "sink.hw0" not found"
with a wrong audio routing during calls, i will report here a solution for this issue.

Thanks to freemangordon that identified the crash of ohmd daemon, i found that it was crashing after "module rule_engine failed to load but listed in require aborting" since rule_engine requires /usr/lib/swipl-5.6.50/* that, if manually moved in /opt (like in my device since always complaining about free space), sometimes is not available at the moment of ohmd daemon start on boot.

So, take care of ohmd, probably is not running or is complainig about something missing.