One of the most successful tools among those included in Facebook is MyCalendar. It's an application with which you'll be able to keep track of all your important dates.
With MyCalendar you'll be able to import the date of your Facebook friends' birthday dates, in such a way that from the application you'll be able to easily send them a message wishing them a happy birthday. Program and launch reminders that will notify you of their proximity. These reminders can be programmed for a specific data and time of your choice.
You also have the possibility to mark important dates and, likewise, configure reminders for them.
Thus, if you don't want to miss any important dates, you should consider downloading MyCalendar for iPhone.