I’m not sure why you’d want to do this, but ProRemote is an iPhone app that lets you control Pro Tools.
ProRemote has been submitted to the AppStore. The price for the full edition is $149.99 US, the light edition is $39.99.
Here’s a link to a demo with audio.
If you’re a Pro Tools, let me know if you can see spending $150 on a program that lets you control Pro Tools with an iPhone.