“According to a research paper, « What Data Do The Google Dialer and Messages Apps On Android Send to Google? » [PDF], by Trinity College Dublin computer science professor Douglas Leith, 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. « The data sent by Google Messages includes a hash of the message text, allowing linking of sender and receiver in a message exchange, » the paper says. « The data sent by Google Dialer includes the call time and duration, again allowing linking of the two handsets engaged in a phone call. Phone numbers are also sent to Google. »”

Source : Messages, Dialer apps sent text, call info to Google • The Register