tell me which provider has an integrated single signon service for all of those above? Which provider has apps for their service for all major OS'es (including mobile), and is mostly free (or low cost)?
You might not want to be tied to Microsoft but Google is not the only option.
Edit: Overlooked the comment about Apps. Microsoft offers apps for mobile, but not Linux. Although even on Windows I use the browser to access the services which will work on Linux.
What's needed is a syndication of data, and inter-operable apps. Like how xmpp worked. But of course, all vendors don't like this, because it turns themselves into a commodity.