From The Register [theregister.com]:
According to a research paper, "What Data Do The Google Dialer and Messages Apps On Android Send to Google?" [PDF [scss.tcd.ie]] Google Messages (for text messaging) and Google Dialer (for phone calls) have been sending data about user communications to the Google Play Services Clearcut logger service and to Google's Firebase Analytics service.
Google offers no way to opt-out of this data collection. Both pre-installed versions of these apps, the paper observes, lack app-specific privacy policies that explain what data gets collected.