Me too: no speaker sound from Experia Arc s
Hmm. After being told off quite a few times for not answering the 'phone, I wondered if I had a really quiet sound track as call-tone. No. Chuck Berry!
Tried playing a few tracks. As with a few above, fine with phone jack in and through pods, but no sound through internal speaker. Have already tried the fluff and reset (and volume!).
I suspect that the contacts inside the jack socket for external earphone are not reconnecting after removal. Bally nuisance.
Sort of warming to know that I'm not alone; thanks you guys!