Doing an in-place upgrade in on-prem vs internet has no difference and it works similar. For in-place upgrade on internet, you would need CMG.
The only difference is that, you cannot do remote control using ConfigMgr for internet based client with 2006 version but they continue to deliver the status messages for the deployment to the ConfigMgr for reporting purpose.
Regards,
Eswar
www.eskonr.com
If the response is helpful, please click "Accept Answer" and upvote it.