How can you disable the auto startup of iTunes when connecting an iPhone?

If I remember correctly there's on option that says "Open iTunes when this iPod is connected" on the screen which gives details for the connected iPod. Have you unselected this?

If you go into the Preferences of iTunes (iTunes -> Preferences on OS X), on the Devices tab, there is a checkbox that you can select to prevent devices from automatically synchronizing. This still allows you to manually sync the devices should you choose to do so.

"You can also click on the CTRL + SHIFT keys when starting iTunes and keep them pressed untill you get something from the sort of ""iTunes is running in safe mode"". Then click on the Continue button.

You must keep the ctrl+shift buttons pressed until iTunes detects your iDevice. Then simply untick the “Automatically sync when this iPhone/iPod/iPad is connected” option. Finally click on Apply in order to apply the changes."