But I will grant you that "The Bells of St John" is a lot harder to explain. All I can come up with is that the Tardis phone is what called him back to action from his self-imposed exile which started the whole storyline off, but I'm not sure that's worth naming the whole episode after. Ah well. It's something else for us to spend pages and pages speculating over, if nothing else.
... it's a red herring or something that will make sense later and yada yada.