Online calendars

I have a calendar in Outlook, one on Yahoo, one on Google & one on Windows Live.  They are not coordinated in any way; I have the birthday list on Yahoo, & a daily prayer set up on Google; not sure what I have on Windows Live, and nothing set up on Outlook.    I send reminders to myself, but I never set up sharing.  I recently started using the Cozi Home Calendar. I added some events today & downloaded the iPhone app. I like it, but I am only using it for a personal calendar.