I'm using RunKeeper and you can programme in different distances and intervals. I haven't used the pace alarm yet, you might need to upgrade to the pay version for that. The free version is pretty easy to figure out, maybe just download it and have a play and see if it does what you want it to?
I'm about to get back into running - inspired by the marathon and sunshine!
I've come up with a plan based on a few different ones. Used to run with a Garmin which I could programme to do the different workouts e.g. run 400m fast, 200m walk etc, but that has gone kaput and I can't really afford to replace it.
I like the look of the apps which beep at you as you are running round to change pace etc. Does anyone know of one which you can use by uploading your own programme?