Having used my phone for a couple of hours, I can confirm that the sound is excellent. I was listening to music on the subway all the way home from the store (luckily I had a micro SD with a bunch of music in my DSi). The sound from the speakers can fill a room.

The first time I used the phone was to call my wife in Finland and the sound clarity was insane compared to the iPhone3G I've been using for the last year.