The ss says he has callled Jack's number only once before, when his divorce comes through. Jack apparently misunderstanda the reaosn for the call so drives north as in the movie. But if they talked, why would Jack take off without asking Ennis, who was there on the end of the phone, if he wanted him to come? If as in the movie he sent a card, and it was as brief as his usual messages, Jack is much more likely to have got the wrong idea. I don't think they called one another at all otherwise because it was too dangerous - you never know who's listening in; too awkward if one or the other rang and Alma/Lureen answered the phone; people didn't use the phone nearly as much in the 60s as they do now.