I absolutely adore my Sony 810i ! I've been using it exclusively for music, taking it to school and work all week now actually, with really no complaints. Here's the deal though: Gapless, no. Hiss, definitely audible when nothing is playing BUT, once the music is on, it's all good. Plus, if you debrand (different from unlocking) your phone, there are different audio drivers available for it, which are said to eliminate the hiss all together, as well as increase overall volume (which I don't have a problem with personally) as well as improve sound quality in general.
I've not gotten into the debranding thing yet, but I will eventually. The other part of the deal, which really needs to be considered is that anyone whom is as obsessive about audio quality as we on this forum are, should NOT consider ANY phone (at this time anyway) as a substitute for a dedicated DAP. I can honestly say that the sound quality of my 810i playing Mp3's is really, really good, but I can certainly tell the difference between it, and my iPod, and most definitely my iRiver H120.
However, it's MORE than good enough to use for taking to school and work, when the bulk of that time is spent on the train, and intensive listening isn't required or happening. I use my JVC Marshmallows with it, through the headset adapter (because I do take calls when listening) and with a tad of EQ'ing, the SQ is really quite good. I can even discern low and high quality bitrates.
Also, the camera on the 810i kicks ass for a phone/camera. And the phone its self, just rocks. Great reception, incredible GUI, so easy to navigate and a pleasure to use. It's really the first time I've been impressed with any cell phone I've bought, and I've been in the game for about 16 years.
I got it about 2 months ago, for $65 with a new Cingular contract.