Where to I put code accessible in all model?

Even though I've been "playing" with RoR since before 1.0, I've never got a good grasp on where you put code!

Code or helper method placed in helpers can only be called from views, if I'm not mistaken.

Code that is specific to a model or controller is also a no-brainer - but what about code that you want to share in different models/ controllers.

What if I have a function unformatPhone that I want to call in a model's before_save event - where to I stick it so that it can be called by all models and maybe even from a view?

Is my only choice in the application_controller? Is that a good choice?

The unformatPhone example may be trivial since it is only a regexp replace, but what if it is something more complex. I looked around for something that would set the case of proper names and found something on github (GitHub - tenderlove/namecase: Properly case people's names) which is a class. Where do I stick that?

If anyone can point me to a good tutorial on where you put code, I'd be thankful.

To share code between models, you have the same two choices that you have for sharing code between *any* classes (remember, there's nothing magical about models):

1. Put it in a module and include it in the models you want to use it, or 2. Create a subclass of ActiveRecord, put the code there, and have the models inherit from that.

or 3, decide that this code deserves to be in a class of its own.