Yes. In fact, the full view of Yahoo! Calendar is the place to look to find extra details for an event, like a phone number, an address and more. To use it, just click Calendar from the list on the left side of your Mail page.

Events you create in the full Yahoo! Calendar will be displayed in the calendar timeline strip at the bottom of your Mail page, and events you create right in the timeline will, accordingly, show up in your full Calendar. Of course!