I upgraded my iphone 3GS to iOS5 last night. Now all the events have gone from my calendar. Also, the '+' icon to add new events has disappeared. I only used the Calendar app on the iphone itself. I do not have any other Calendar software. What has happened? This is really frustrating, as I have lost all my appointments, and is adding to my general disappointment with iOS5.
Well, i solved it in typical counter-intuitive fashion. I chose NOT to sync my calendar with icloud. This removed the calendar from my iphone, it appears. By turning this back on (Settings>icloud>Calendars ON), I got my Calendar (and the events and + button) back. This means I have to use icloud if I want to use the calendar app.