Audio learning can be a great brain exercise. This is a Morse Code practice test generator which can generate random 5-letter words, and send them in International Morse Code using your iPhone speaker. The WPM (words per minute) speed can be easily set. You can independently set the dot speed (for the Farnsworth method), and tone frequency. You can also configure the number of possible letters and numbers used, as well as customize the sequence of letters and numbers from which the test words are generated (for training similar to the Koch method). You can either show or hide the test words as they are sent. 100 letter (20 5-letter words) are generated at a time, making it easy for you to score the percentage you've learned to copy correctly.
Other Morse Code applications by HotPaw Productions in the App Store include MorseDecoder, MorseKey, and Text2Morse.