You can develop your app so it uses generic settings, or settings that are specific to each phone. If you have phone-specific settings, you can choose to store them in the phone's config file, or have the user enter the settings via your app. This guide discusses how to choose the best solution for your app.
If your app relies on information that may be different depending on the phone that is using the app, then you'll want to define settings for the app to use.
Settings stored in the phone's config file
The appconfig area of each phone's config file can include one or more settings for the app to retrieve and act on. This is a good way to publish settings because they are managed with the rest of the phone's configuration information, and they will 'survive' a factory reset (because the settings are stored somewhere else).
In development, those settings can be entered using the development web page or the CGI.
Settings entered via your app
If your app includes data input, then that information is stored and retrieved as indicated in your app.
Remember information gathered this way is deleted during a factory reset. So, if you are collecting a small amount of information that won't be too discouraging if a user has to re-enter it, then this method is fine. Otherwise, you should manage your app's settings along with the rest of the phone's configuration information, and publish it in each phone's config file.
The following example uses the digium.readFile and digium.writeFile methods to store local settings.