MP3 Media Player: Pandora will have more choice. Considering the build-in speakers: iPods suck very hard. Really crappy sound. Didn't hear those of the iPhone, but I'm betting they're the very same.
While the Pandora will have better codec support, I'm going to be viewing so few videos on the go that it's almost a moot point. I intend to use the speakers only for games (primarily retro, in which case I don't need high quality speakers on such a portable unit). For music, where sound quality matters, I don't see myself using the speakers on either device.
More portable: How portable do you want it to get? The iPhone does not have gaming controls, all kinds of functional ports, dual SD slots and a full keyboard, by the way.
More portable than the Pandora. Let's face it, the Pandora isn't exactly tiny. The iPhone is portable enough to become a device that I could carry around with me all the time. I certainly don't see the Pandora in that light (unless I want a rectangular bulge always sitting in my pocket, which is personally too much for me in my day to day life).
As per my original post I'm looking at the iPhone this way assuming that the iControlPad works just fine with it (that takes care of the gaming controls part). As far as ports are concerned, the main things missing from the iPhone would be USB Host & TV-Out. These two are ones to seriously consider as one of the Pandora's greatest advantages is the ability to use it as a "Pandora Cube" (to borrow Craig's words). I'm not going to lie and say that USB Host & TV-Out are 2 big pros for the Pandora.
iPhone has a solid amount of storage space on it, and I don't see myself using SDIO, so the dual SD slots won't really be missed.
The QWERTY keypad will be missed for internet browsing, I'm not going to lie about that.
Cool OS: Pandora will have so many OS's you WILL find a very cool one eventually. The iPhone has, only one OS.
All I need is *a* cool OS, so it's not a negative in my books if the iPhone only has one (cool) OS. I'm not too much of a stickler on a neat OS, but it can be a nice perk. I'm sure with due time I'd find a nice Pandora OS, but it's also nice to have a great one right from the get-go, you know?
More mainstream and commercial quality games: Pandora can emulate whole libraries of those. And it will have new games also. Maybe not super duper 3D games, but who cares. You want a commercial gaming system for that. Nintendo DS and Sony PSP are WAY beyond what the iPhone has to offer. Commercial releases will find their way to the Pandora, eventually. Maybe not in large quantities, but still.
Assuming jailbroken, iPhone also should be able to emulate whole libraries of those. And it will have new games also. Super duper 3D games (and 2D ones, of course). I have a Nintendo DS for commercial gaming, but what's the harm in having more commercial games for a device? It's nice to have it all there as an option in one device. I think this one is a clear-cut iPhone win?
Concrete release date: We will see about that. First thing to learn in electronics and gaming land is: do NOT trust release dates.
I trust Apple a lot more with release dates for the iPhone than I do the OpenPandora crew with the Pandora, and at this rate I think we'll see the iPhone 3GS a lot sooner than the Pandora
Just to clarify, I'm not trying to come off here as saying iPhone 3GS > Pandora. There's clearly a lot that the Pandora brings to the table that would be sorely missed with the iPhone 3GS (TV-Out, USB Host, QWERTY keypad, nice scene, etc.; in addition, this comparison is assuming that the iPhone 3GS is jailbroken and works just fine with the iControlPad), and I don't plan on cancelling my pre-order and jumping on the iPhone 3GS bandwagon. It's just that now there's enough pros with the iPhone 3GS for one to go "Hmm..." at the idea of comparing it with the Pandora, and I'm simply entertaining that idea