Homescreen is the most prime real estate/ important view of the mobile device and gets more page views than any other page/application view. User always navigates to other applications from the homescreen. Homescreen's impact on a user is much more than all the other applications put together. Homescreen is the first thing the user sees after powering on the device.
Hence it is very important to be very careful while making use of the homescreen. The sensitivity and importance of the homescreen can be gauged from the fact that Nokia has guarded the sanctity of the active idle/homescreen zealously until now. 3rd party developers had very limited control/access to the homescreen space. Only through partnering/valid business case evaluation could one get access to the active idle.
See limitations from:-
Going forward from N97 onwards, Nokia has provided the Homescreen Publishing API, using which 3rd party developers can place their widgets on the homescreen.
With earlier versions the user can always do direct screen drawing to draw their content on the homescreen, as detailed on the link How to display ticker on active idle .
Homescreen usability guidelines are
Allow user choice to place/remove application from homescreen
Since the homescreen is the main view of the mobile, it is very important to take due consideration in deciding whether you really want to use up that space for your application usage. The user should have a choice to decide whether they want to see the application on the homescreen or not.
Do not hamper existing functionalities
Make sure that if you are modifying the homescreen, or using that space to display your content, you do not hamper any of the existing functionalities. The navigation bar which allows faster access to applications, ability to use the center key pad etc, should work as expected. The user should be able to navigate to the menu/default applications with the same ease/consistency as they were earlier when you had not modified something on the homescreen.
It is imperative that high priority events like incoming call/message etc are handled the same way as they were without your application on the homescreen. The user should be able to accept/reject the incoming call etc. Do not hamper the existing navigation mechanism or jump views between your application main view and homescreen repeatedly as this could confuse the user.
Avoid flickering/sluggish UI response time
In case of placing the content on the homescreen it is imperative to make sure that the homescreen response time doesn’t get affected because of your application using that space. You should make sure that while drawing the content or on updates to your application widget, there should not be any flickering and the user should not see any inconsistencies from an overall look and feel point of view.
Using the ScShortCuts Engine Wrapper API, 3rd party developers can make changes to the soft key on the active idle to display shortcuts to their applications instead of the native applications.
Details can be had from:-
--- Added by Mayank on 26/06/2009 ---