Editing items in quick pick dropdowns

[Viva Terlingua]

When you enter a new task or new appointment, there is a dropdown list on the subject line with items such as; Call, Meeting, Work on, Buy, etc.

Does anyone know how to add or delete items from these lists?

Using WM 6.1 on a Treo Pro, but I think the question/solution would be universal for all WM devices.