SMS is baked into Hangouts. Nearly everything is centered around Google Now. Even if you don't use gmail for your email, using the default email/calendar/contacts app for any email/services means data is extracted from them.
SMS info is wrong. You can use Google Messenger for SMS/MMS without signing in with Google account. SMS integration within Hangouts is optional and you have to check a box to enable it. Google Now is optional but makes no sense without Google authentication since it does correlation for the predictive notification. Except for Gmail that requires authentication pretty sure calendar/contacts don't and stores locally if you don't. Apple mines your data too and even has Beacon to track you and spam you with ads.
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