Cellphone sales are falling, manufacturers have announced thousands of layoffs and wireless carriers are finding it harder to acquire and keep customers.

It seems like another tale of “recession bites industry,” but there are signs that this downturn is masking something more fundamental: that the cellphone industry’s best days are behind it.

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. “I don’t think anyone would argue that the salad days of the wireless industry aren’t over,” he said. He added that in terms of subscriber growth in North America, “we’re awfully close to saturation.”