Voicemails not restored from iCloud?

My wife and I both restored our new iPhone X's from iCloud backups (created from iPhone 7 Pluses running iOS 11). In both cases voicemails did not restore. We activated our new phones using the included SIM cards, not the previously-active SIM cards from our 7 Pluses. What does iCloud back up? - Apple Support mentions that the voicemail password is restored if the same SIM is used, but makes no mention of the messages themselves. I was under the impression that voicemails restored from iCloud as well as iTunes.