As I work on the MacBook Pro, I like to have my phone next to me on the desk playing a podcast or some sports talk radio. Built in speakers are fine for this as talk doesn't have a lot of dynamic range. My phone is also an information appliance. It's faster to bring up the Amazon app on iPhone and Nexus One than to open a browser window sometimes.
The speaker is on the back of the phone, near the top. So you lose about half the volume if you rest the phone on its back. And you lose the screen if you put it face down. At left, you can see my improvised ceramic Nexus One dock.
Note that with multi-tasking, I can listen to I-Heart-Radio and have my home screen available for other tasks. I can pick up the Nexus One and use another app and the show keeps playing.
The iPhone has its speaker on the bottom of the device. This has repeatedly bugged me since I got it. Because sometimes I'll be listening to a podcast and playing a game like Farkle or Scrabble or Doodle Jump and I want to rest the bottom of the phone in the cupped palm of my left hand, but that blocks the speaker.
It's a small thing, but the HTC crew got it better with speaker placement. Nor perfect but better. If they moved the speaker slot up 1 cm to the curve at the top of the back of the phone, I probably wouldn't need the ceramic dock.