Guest access is released 100% WW in service

Just to add: group owners can also add external guests through your groups via our apps available for iOS, Android, and Windows Phone.

Billions of email users are now available to you to add into your groups to share emails, calendars, SharePoint document libraries, and more.

iOS: https://itunes.apple.com/us/app/outlook-groups/id1027125154

Android: https://play.google.com/store/apps/details?id=com.microsoft.outlookgroups

Windows Phone: https://www.microsoft.com/en-us/store/p/outlook-groups/9nblggh1pbr5

Instructions for adding guests in the Outlook Groups apps can be found here under the section, Add guests to a group using the Outlook Groups mobile app — group owners only at https://support.office.com/article/3b650f4a-5c9b-4f94-a1bb-0cca4b1091de