Let me try to describe something in my mind for quite some time.

The mobile phone only has one purpose : to help its owner in doing some tasks. Its goal is not to provide access to some ecosystem.
Each person will have different tasks he would want the device to do.

Mainly, the kind of tasks done actually revolve around communication, media creation/sharing/playing, localisation and navigation, gaming.

Each time there is a need, the solution usually chosen is "create an app". I think this is where it starts to create problems in usability.

If I try to follow Jaakko's articles, we have to think how to answer the needs without taking the old paradigms as the only ones. In this case, the application is a desktop paradigm of the way the underlying system works (running programs). In any case does it mean that this low level constraint must be visible on the UI level.

There has been some works in several ecosystems to blend the application together (like adding a share on twitter/facebook link in the camera app, or the contact hubs).

This should be taken on a higher level, removing completely the applications from the user level, and increasing a lot the intergration between those services.

Usually, on the phone, the user follows a task flow, and doesn't work in a single app.

For example :
* receive SMS. Get notification
* Open the SMS app : A friend asks if you want to go see a movie
* Open the movie app (or browser), search for the current movies and time
* Go back to the SMS app : answer the friend

An other flow:
* Have an alarm reminder of the coming meeting with a friend
* Open the mail app, and search the mail were a friend gave you the restaurant website's URL for tonight
* Open the website, find the address
* Open the navigation app, to drive to this address

On most systems, you would have two apps open : SMS and movie/browser (or 3 for the second example : Mail/Browser/Navigation).

But... user are multitasking a lot, as anything can happen during this task flow. You were cooking while doing this, and have to go back to check the recipe ? Someone calls you ? In the movie app the director name reminds you of a friend you had to mail a file ?

Mix some simple tasks for some time, and now you have several apps opened. The broswer app is shared between two task flows (the movie, and the recipe), the mail app two (you were writting a mail, but some other mails were received in the mean time and you read them), ....

At the end, you have some task flows, and a multitasking view that doesn't represent it anymore.

What I think would be better, would be that app were hidden behind "views". Then the multitasking page would now list the task flows, and not anymore the apps used.
A task flow would be a chained list of "views" used to get to the intented result : the task being complete.

That way, you could add a new task flow, interrupting the current one, when something happens, and then be able to leave it there for some time, while switching from one flow to another.

I am not sure if this is well explained, and how to do this to be usable (that's were someone like Jaakko would help a lot!). Ask me if you want to rephrase some part, or add a drawing.