If I buy an iPhone app will I have to re-purchase the app if I get a new iPhone? I upgraded from the 3G to the iPhone 4 and forgot to backup and transfer my apps. If I attempt to purchase apps that I have previously purchased, will the Apple store charge me? Or will it recognize that I have already purchased the app based on my apple ID?
No, you will not be charged. You can re-download them in iTunes or directly on the phone. You'll have to hit the "buy" button, but after it starts downloading, you should see a message saying you already bought it once. The alert box includes a button to go ahead and re-download the app, which you will then not be charged for.