I'm puzzled as to what proprietary interoperability standards people think Apple use. Other than Facetime/iMessage I can't really think of any. IChat used to use jabber.

Their mail uses IMAP, calendar is CalDAV, contacts are CardDAV, cloud storage is WebDAV.

They don't support Microsoft's mtp at the os level but they do support the ptp subset in iPhoto.

Jolla's support of all these open standards is dismal unfortunately.