https://www.theverge.com/2018/5/29/17405420/messages-icloud-ios-11-4-imessage-syncing-apple-iphone-feature

It’s been a long time coming, but Apple is finally launching its Messages in iCloud feature today with the release of iOS 11.4. Messages on iCloud was announced almost a year ago when Apple first showed off iOS 11 at WWDC 2017, and now — on the eve of the announcement of iOS 12 next week — it’s available to all users.

Messages on iCloud is kind of complicated, but here’s what it does: