I managed to use my Office 365 contacts on a GXV3240. But mails were also synced which was not so interesting. And it had to be done on the touchscreen in an app and could not be done from the web gui.
Turned out to be buggy as well.
If I’m not mistaken you cannot use LDAP to connect to O365? Would it be possible to implement an O365 contacts sync from the web gui? But only the contacts.