When a message arrives (Text or Email), sometimes the Notification (Ringtone/Vibrate) is activated.
Other times (most times) the messages arrives without any notification.
Any help in fixing would be appreciated.
I haven't had that issue. When it is in silent or vibrate I don't get notifications but when sound is on I do. I think I set it that way but I really rely more on the flashing light that the vibration. Though part of it may be a time thing. You only get notifications every so often so it may be that you are checking them before the notification would go off.
After Googling, I found it is a bug that should be fixed in an upcoming update:
http://code.google.com/p/android/issues/detail?id=4190