Someone has finally made a WP7.5 MIDI controller app Smiley
http://www.windowsphone.com/en-US/apps/24454ae4-dee0-45db-9fd9-f4f278646193

The interface isn't perfect yet and there really is no need for 20 pads. 16 pads is the most common setup for midi pad controllers.
Hopefully this person keeps developing the app and integrates XY pads and piano keyboards etc.
I'd love to see MIDI CC messages being sent according to how the phone is tilted too.

It's still great to see someone actually make an app like this for WP7.5.