Exact same problem here. iPhone 5 16 black. No sound from bottom speaker straight out of the box. Earphone works fine, headphones work fine when plugged in, even the vibrator works just fine. Tried everything this thread suggested, including the Q-tip trick, which did absolutely nothing for me.
So today I had to take a real late afternoon flight back to LAX from a business trip - full flight, middle seat, all the way in the back between fat people FML style. Then I was stuck in Friday LA traffic for almost 2 hours before I finally got home. Which was ALL chill because today was iPhone 5 release day, and I had one in the mail waiting for me.
Then 15 minutes later...\/\/ T F Apple?!??!?!??! *flip table*
It was too late to call Applecare so I called Apple iPhone sales at 1800MYAPPLE, which was a complete waste of my one hour. So I will have to call Applecare tomorrow, or just go down to my local Apple store and ask one of the "geniuses". But what I'm real concerned about is that if I have to mail back my defected phone for a replacement, what am I gonna use in the mean time? Cus the moment I turned on my new iPhone, my old sim is deactivated and it's not like I can just take out the new sim and put it into my old iPhones since it's the new NANO sim! So do I have to contact AT&T too now, for like, a loner phone or something? Ay ya yay~
Either way, I really hope the most valuable company in the world can have a simple solution for a situation like this tomorrow when I call in.