Should I get toast displayed by the OS when my app is running in the foreground? I can not get clear information about this. I think it's rather an issue.
You can't get toast notification when your app is running in foreground. Push notification service only sends notification when the app is in background. If you want to notify the user in foreground you should have to use custom notification.
One implementation for this can be found as ToastPrompt in Code4Fun toolkit. The link is here:
http://coding4fun.codeplex.com/wikipage?title=Toast%20Prompt