No sound through handset speaker of Nexus S Suddenly when I was playing music on my Nexus S it stopped playing all sounds through the handset speaker. It still works though if I use an external headset though.

I don't really have that much knowledge of the Android internal workings to see what the problem is, although I tried rebooting it.

I also can't really leave it for warranty repair because the boot-loader is unlocked (although I later reflashed back to the stock ROM).
I just saw this googling around, maybe it could be of help to you:


  okay, I had the exact same problem. My speaker suddenly stopped
  working even though the ear phone plugin was still working good. I
  also found that sometime the sound came back but it is very weak,
  barely audible. and then it would disappear again. What I did to fix
  the problem is to open up the N1, disassemble instruction is on
  youtube. Open the the 3 screws to remove the board with the attached
  speaker from the main board. clean up the speaker attachment surface
  really good. Then reassemble the backboard and its speaker together.
  Then the sound came back loud and strong.
  
  My guess is that the contact of the speaker could get dirty and
  limit the electric supply to the speaker hence it didn't work
  properly. By cleaning the surface I helped to get the current going
  again and the sound came back. Hope that this could help someone since
  this problem had driven me insane for a while.


I found this on the following website: http://www.nexusoneforum.net/forum/nexus-s-general-discussion/12468-external-speaker-not-working.html.

Cheers, and I hope this helps.