There are two possible options here that may work. I haven't tried either of them yet but have seen reports of both options working.

1. Use a cable to connect from the iPhone to the composite video port of the Smart Board. I think this is the correct cable Apple Composite AV Cable - Apple Store (U.S.). If your smart board has component video connections there is also a similar cable with that connection. This may not work in all cases as there appear to be some apps that do not support video out this way. It is also a one way connection in the sense that any touches made on the SmartBoard are not reflected back to the iPhone.

2. There is supposedly a piece of software that would allow two way communication but I can't seem to find the link at the moment. Will post back when I have more.

Edit: The app that I was thinking of does not exactly allow two way communication between the iPad and SmartBoard. Essentially you are using this program to control the computer that has SmartBoard software installed. Useful but not exactly what you want to do. Looks like we are limited to option one for the time being.