Blackberry 8100 User Manual page 155

Custom address book field data is not appearing on my computer
You can only synchronize the information in a custom address book field with a text field in the email
application on your computer. For example, you cannot add a contact's birthday to a custom address
book field on your BlackBerry® device and synchronize it with the email application on your computer.
The birthday field is a date field in the email application on your computer.
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