A simple enough app, but it’s free and might be of use to you.
OSC Piano is a free OSC control surface with a simple piano interface for iPhone / iPod Touch.
It supports sending Open Sound Control messages over a Wi-Fi network using UDP protocol.
The application allows to remote control from software and hardware that implement the OSC protocols such as Pure Data, Max/MSP/Jitter, Max for Live, vvvc, Isadora and others.
Also, you can convert OSC date to MIDI data by using OSC Piano Server on your mac.
OSC bundles are
* Note Bundle *
oscP/note i (0~127)
* Accelerometer Bundle *