Calendar syncing issue - icloud and yahoo calendars

[mcgeggy]

I have an iphone 4s and I have to use icloud.com since there is no support for Windows XP. How can I get a calendar entry made on my iphone to appear in both my yahoo calendar and on my icloud calendar? I can get it to do one or the other, but not both. I would like to make a calendar entry on the iphone and see it synced in BOTH my yahoo calendar AND the icloud.com calendar! What am I missing here?