A 25-key MIDI keyboard? Really? You’re telling me you did that before making a nice Accordion Dock? Missed opportunity, if you ask me.

Apple added the ability to connect custom hardware to its iPhone and iPod touch platform last year, so it was only a matter of time before someone made a music hardware interface. Ion Audio, the budget brand of Numark/Alesis/Akai, gets there first, with the Ion iDISCOVER Keyboard. It docks your Apple mobile into a case with a 25-key MIDI keyboard, pitch and mod wheels, and preset buttons for patch and octave changes.

It’s just what many of us wondered when we first saw Apple’s hardware SDK; David Battino even suggested this very idea.

Of course, there is a slight problem. Part of the whole advantage of the iPhone is its mobility, which a huge honking dock tends to kill. (For less money, you could just plug a keyboard into your Mac, or buy a low-end CASIO or Yamaha keyboard.)

And then there’s the fact that most of the interesting music apps on iPhone don’t use MIDI keyboards. Ion has to provide their own app to fill the gap, which also makes me wonder whether this will work with any other software; I’m guessing not, but I’ll find out. Update: Word from the CES show floor is that Ion plans to open this developers; whether that’s anyone or just partners or even decided yet, unknown, though I hope to snag them at NAMM. Us hard-core geeks would naturally have preferred a standard MIDI interface, so you could use unusual sequencing apps with hardware synths. (Never mind; I’ll take a MIDI Command, instead.)

That raises another question, though — all due kudos to Apple for providing a hardware interface. When will we see third-party hardware support on a platform like Google’s Android? It seems the “open” philosophy of the platform would be best served by an open approach to hardware, too, and technically speaking, the job wouldn’t be that hard, thanks to the fact that Android runs a standard Linux kernel. That could allow any kind of controller — mass-produced or homemade — you want.

I’ve got lots of questions about the iDISCOVER, though; I’ll try to track down answers this week at NAMM. I’m not quite sure who would want this particular product, but it does raise some interesting issues about mobile music tech, especially given the earlier discussion this week.

Thanks to Derek Dumais for the tip. Oddly, Ion seems to have their own version of Akai’s mini-keyboard, too; it seems to be white instead of black but otherwise appears identical. (Consumers want white, pros want black?)