It only breaks down because...er....well... the first time it runs out of radioactive material, and yes another time, its gas line gets punctured, but come on. When would any of that actually happen with normal use?
I think the phone box is actually rather spooky though, I mean, it gets smashed up alot considering gangs and youths these days, and how does it get its power?... you should never trust anything where you can't see where it keeps its head (where did i get that from?...)
What about then after it gets transformed on 2 to fly. Thats kewl.
Or on 3, the train