1st of all, Outlook 2010 doesn't require a VPN connection to work, if you're using a FQDN to resolve the Exchange server. I'm on Koodo and I can do this via Hospot with Outlook 2010. I have not tried with tethering, so it is possible that it may not work, but I'm guessing Outlook can't resolve the server, because of a domain or FQDN issue.
In Outlook, when you setup the server connection, do you use the server name or the IP address? Are you on a VPN with your PC, or not? Need to know more to troubleshoot.
You can also go to the Microsoft site here to fully test your Exchange server... https://www.testexchangeconnectivity.com/
Also, you don't need to run Outlook 2010 via Http or RPC, it will run without any of that even if you're not on a VPN. That wasn't the case with prior versions, but it is with 2010.