According to analysts who see the world as made up of the US market, yes: Analysts and investors are beginning to ask whether the industry can continue growing. The challenge is both simple and daunting: how to expand when more than half of the six billion people on the planet already have phones. And even in developing countries where there are underserved markets, subscribers spend less on phones and services. Craig Moffett, an industry analyst at Sanford C. Bernstein & Company, is one of the skeptics.