PsTools
PsTools is a Photoshop CS5 tool for the iPhone, that gives you all the shortcuts to the basic tools right on your iPhone display. Simple connect with your iPhone with your computer via WiFi and start using your iPhone to change the tools you need for a faster and easier photoshop experience. You need version 12.0.4 or later to use PsTools.
1. Run Photoshop (higher then version 12.0.4)
2. Go to menu Edit -> Remote Connections
3. Fill Service Name, Password and check Enable Remote Connections
4. Run the psTools app on your iPhone
5. Insert ip of computer running photoshop and password filled in step3
6. When select tool on psTools you can see the changed tool on photoshop
You can download psTools in the App Store for free.