I haven't extensively compared the sounds of the video and the iPhone pre-3G, but consider they are the same chip. Now, yes, of course, the same chip can sound different in a different circuit, and everyone's setups sound different. Nevertheless, I will say that I liked the sound of the iPhone's headphone jack through my modded SR60s over any of the iPods I've owned or listened to. My switch to the iPhone was more pragmatic than audiophilically ideal. My plan when I have some disposable income is to use the iPhone for on-the-go listening (unamped through KSC75s and maybe the PX100 someday) and have a 5.5G 80GB for home use. My library sits only at ~12 GB at 320 kbps LAME MP3, but I'm fine with listening to MP3 over lossless. Whenever I did get that 5.5G, I would manage two libraries for the sake of lossless. But until that day comes...
I'm of the camp that doesn't pay all that much attention to their music when going portable. I listen to music to fill up the silence on the train or when I'm studying, but hard listening is something I only do at home. I don't mind going unamped, though the iPhone doesn't go all that loud with the KSC75s. I've been forced to employ playlists with this device as opposed to carrying my entire library with me. I normally prefer not to have to choose the music I want to listen to and not have some selections I feel like listening out of the blue, but it's something that has been imposed on me by the forces of practicality. I'm an album collector by nature, so my albums are normally my playlists. There's nothing really holding me back from making full use of playlists besides laziness.
So, um, yeah, the iPhone might sound the same as the 5.5G.
