Android :: MVC - Application Or Service For Asynchronous Updates

I have data that is to be refreshed from the Internet. Let's call it Model.

What I want to do: Basically it sounds like an MVC model, where the Model is also kept persistent in local (private) storage. The Model and its associated methods are application-wise. There are several Activity's that display and manipulate different aspects of it:

User
navigates across different Activity's
that display Model
from different perspectives. Currently I have a ListActivity for all elements, and an Activity for one element's details
Sometimes Model needs refreshing.
Surely this is done on a different thread. Refreshing can be triggered from several Activity's.
There are several (time consuming) common
tasks that can be triggered from different Activity's
My application loads and saves Model
to private storage when it starts
and stops

My problem: I'm not sure where to put Model and the related tasks in. Also, I don't know what mechanism to use to notify Activity's. Currently I come up with 2 approaches:

Use Service and send broadcasts. Saving to disk is performed in Service#onDestroyed(), so I want to minimize that by binding it to Activity's. At this point, I'm also not sure how to deliver the updated information: whether to provide a getter in Binder, or include that in the broadcast message.
Customize the Application object so that refreshing methods and getters are available globally. I then perform update from Activity's using AsyncTask. If there are other Activity's that are behind the current Activity, they will update in onResume() when the user navigates back.

Reasons I'm not using a class with static methods:

I need to save and store Model to disk. Some of the methods need a Context for displaying toasts, notifications, caching, etc.


Also, I don't put these functionalities in an Activity because there are several activities that manipulate the same piece of persistent data.

Below are pseudocode illustrating what I mean:

Using Service:

CODE:............

Make the functionality globally accessible in the custom Application object

CODE:...........

Weaknesses I can think of for the Service approach is complexity, since Binding is asynchronous. And it's very likely that I have to repeat some code because I have both ListActivity and Activity

For the Application approach, the documentation says not to rely on onTerminate() being called.