Q: App to control presentations on my ipad

http://support.apple.com/kb/HT3325

That application does allow you to control presentations on your iPad from your iPhone or iPod touch. What other presentations are you trying to control?

Edit: From the app listing,

Keynote Remote lets you control a Keynote presentation on your Mac, iPad, iPhone, or iPod touch from another iPhone or iPod touch in the room. While you present, view your current slide and presenter notes in portrait, or the current slide and next slide in landscape. Swipe forward to advance and swipe back to return to the previous slide.

Your best bet if you need something universal is an application like this:

http://www.remotemouse.net/iphone.html

It basically turns your iphone into a remote trackpad for your computer. As far as using the iPhone to control the Ipad, aside from keynote and what I showed you before I think you're going to have some trouble. I'll search around.