AT&T has said it wanted to acquire Time Warner in part to make TV advertising more targeted, as with the Web. If history is a guide, it may take some time.
Rival Verizon has also made several huge digital ad acquisitions over the past few years, but it's moved slowly to fully realized their potential.
Former Verizon media chief Marni Walden said that giant companies tend to move slowly and cautiously, and are often siloed.
Until a few months ago, Marni Walden was Verizon’s EVP and president...