I've got a YH-920 GS as well, and I'm considering to start a new port. According to my internet research, the YH-920 and YH-925 should be quite similar, except the colour display and possibly another chip to display pictures for the 925. Since both are PP5020 based, I'm quite optimistic that we can achieve something quickly here. Other components are already well-known (e.g. Philips FM tuner chip) or well documented, like the AKM audio chip, and hopefully we could adapt linux drivers for similar AKM chips.
Dan, I've noticed your YH-920 wiki entry; over the weekend or beginning of next week, I will try to extend it with PCB scans and HW component info.
BTW, a simple LG phone data cable could be a cheap cable substitution, except that the wiring is different; I could let you know early next week, in case the 820 cable does not work for the 920.