Will a Ipad2 hook up to the new p-105 by yamaha so that you could use garageband thus giving yourself more "voices"?
It's a good question. The P-35, P-95, and P-155 will work fine, with any of a number of adapters. But the P-105 doesn't have standard MIDI ports, only USB. Most USB MIDI keyboards can connect to an iPad using the Apple Camera Connection Kit, but Yamahas are generally not "class compliant" meaning they need custom drivers, and unlike a Mac or Windows PC, there is no way to load the custom drivers on to an iPad. So I certainly would not assume it would work. I'd be curious to know if anyone has tried it.
If nothing else, you could probably get it to work by converting the P-105'[s USB port to standard MIDI ports (with iConnectMIDI) and then use a standard MIDI adapter on the iPad. But you're talking about something in the range of $250 worth of adapters to make it work. You'd probably be better off picking a piano that just worked in the first place, like one of the other Yamahas or the Casio PX-350 you mentioned.
EDIT: It sounds like someone tried the P105 and it worked...http://forums.musicplayer.com/ubbthreads...Charge_iPad_too