My wife and I have two windows phones with separate windows live ids. We want to share calendars. This is especially important for us with all the doctors appointments that my son has.
The 1.0 version of Windows Phone 7 does not allow you to use the calendar sharing in either hotmail or live mail. I have confirmed this with Microsoft. (See calendar syncing). It also does not allow you to do calendar sharing with separate gmail accounts. You also cannot share a single hotmail calendar when you have two separate live ids. Google to the rescue. You can use a single gmail account and link it to two phones.
Here is the process:
1. Create a gmail account.
2. On both phones, in the windows phone settings add the gmail account. Under content to sync, unselect everything except Calendar.
3. On both phones, go to the calendar, click on the elipsis at the bottom and click on calendars. Disable the windows live calendar and make sure the google calendar is on.
That is it.