The following Android devices are known to be incompatible with the calendar integration feature.  We will update this list as we receive feedback from our users:

• Kindle Fire: It appears as though Amazon removed Android's built-in calendar database, or at least blocked access to it.  This means that Ultimate To-Do list cannot read or write calendar events that can be seen by other calendar apps.
• Blackberry Playbook: Ultimate To-Do List uses the Playbook's Android emulator, which does not have access to the Playbook's built-in calendar database.