Apple's iTunes Store keeps track of your iOS (iPhone, iPad, iPod touch) purchases and typically won't charge you if you re-download the same software again using the same account. You will need to click the "Buy" link, but Apple's iTunes should not charge you. (Please understand that we have no control over Apple's online store policies.)

Note that Apple's iOS App Store and Mac App Store are separate, and purchases on one do not include purchases in the other.