there is a c25k app...put c25k in the search and it will show you a couple of options...
I also found an app called something like ultra timer, and you can set it for intervals...it makes a sound/changes color at set times (you choose and can set many timers) - i like this behind music
example: run when it turns green (with a sound alert of your choosing)
and then walk when it turns red (with a different alert sound of your choosing)
i'm no longer doing the c25k, graduated, but because i do long runs - i still prefer intervals in my running...this works perfectly..i set it to start then choose a playlist to play over it...you can hear your music and the sounds will play behind it