I'm trying to figure out the best way to meet a user's (Corp-A-User) request to share their calendar with someone at another company (Corp-B-User). We're running Microsoft SBS 2008 with Exchange 2007 and SharePoint. The remote user is running Exchange, version unknown.

Corp-A-User wants to give the Corp-B-User the ability to create appointments on Corp-A-User's calendar. This will naturally require sharing of Free/Busy information. Corp-A-User naturally lacks the vision to seen ANY problem with giving Corp-B-User full access to their calendar. But, I see the problems with that and would prefer that Corp-B-User have only the ability to see Free/Busy and create appointments.

Most of the external publishing options that I have thought of, such as WebDav, allow displaying a user's calendar, but there are problems with security and the ability to create appointments. Right now, I'm thinking the cleanest solution would be to use a Google calendar along with Google Calendar Sync for the two user's Outlook clients. But, I'm not sure if there isn't a better way and I hate teh idea of pushing a corporate calendar up to Google. Not to mention the issues likely to pop up from the multiple sync paths.

Does any one have a good solution for this scenario that would be willing to share what they use?