I want to add interval running to my mornings. I just got an iPhone5 and want to use an app. What have you used and liked?

I don't really want to think about my running - just want to have a nice little voice tell me what to do. I enjoy being elsewhere. Just want to run intervals for 20-40 minutes at day over a course of about 3.6 miles that is right around my home. And I want to do some interval training - seems the press is focused on that, I and I kinda like the idea of it.

Any recommendations?