MathU RPN 2.2 for iPhone
MathU RPN is available exclusively via Apple's App Store. It is currently available for $19.99 USD. Use iTunes Store or your iPhone to access the App Store and then search for "MathU".
Like all iPhone applications, the only way to get MathU RPN installed in your iPhone is via the App Store. To purchase, open the App Store within iTunes or on the iPhone. Search for "MathU". Installation happens automatically when you purchase MathU RPN through the App Store.
When you click the App Store icon or the link above, the App Store will automatically open within iTunes 8 or higher. If this does not work, open the App Store on your iPhone or iPod touch and search for "MathU".