Take a look at this cool Windows Phone 7 application with landscape layout that Jason Zander made. It's called Tip Calculator and makes it easy to figure out your bill in a restaurant or for a cab ride.
When the user rotates the phone we want the layout to change to match the new dimensions. This is also fairly straight forward to implement. The first step is to have an additional column in the LayoutRoot which can accommodate the totals data. When the phone is rotated into landscape mode, we will move the TotalsGrid into the second column adjacent to the NumbersGrid.