I taught my son how to tell time using the iPad app, Jungle Time. I bought it for him when he was five but he wasn't ready for the concept past "o'clock". I reintroduced time to him again this summer before he entered first grade. He had outgrown the need for the sounds (can be disabled) and the animal faces. He was bored with it in one hour because he had mastered time.
Don't be too impressed, we only worked on o'clock, :15, :30 and :45. Still he learned quickly, either from the impressive app interface or the bribe that he could play with my iPad when he had learned to tell time.
Jungle Time has five learning levels and he completed three levels within an hour. Though this app has many time learning capabilities, we only used two of them. He learned from "What time is it?" and "Set the Time".
I have no intentions of letting my son play with my iPhone (because it attached to a major artery) but I do like apps that are universal. This isn't one of them. You'll pay $2.99 for the iPad app and $.99 for the iPhone version.