the author of this app says:
How many times have you forgotten someone's birthday or your own anniversary? If you answered one or more times, you need DueDate to help you keep track of special occasions.
You can import information from the built-in address book and even export to your MemoPad. DueDate also works with the ToDo, AddressBook and DateBook applications on your device.
If a date is important enough to write down, it is important enough to have your device notify you about it.
This program requires Palm OS® 3.0 or later.