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American Tower Corp. (NYSE: AMT) and SBA Communications Corp. (NASDAQ: SBAC) have enjoyed significant gains over the past year. Actually, make that the past three years. The growth of data usage has outpaced the growth of users in America, and the so-called cell tower owners have reaped the rewards.

Macquarie is saying enough is enough. The firm has downgraded these two cell tower owners and operators due to stretched valuations now that shares have risen so much. American Tower was down close to $20 at the peak of the selling back in 2008, and shares are now above $77. The 2008 lows for SBA Communications was closer to $12 and its stock is now up above $70 per share.

This downgrade is solely a valuation call, and both stocks were cut to Neutral from Outperform. Macquarie is still positive on the business models of these companies, and it even expects strong results for the fourth quarter of 2012 and into 2013. The risk seen is that the firm expects investors to start discounting a 2014 slowdown.

SBA shares are down 1.7% at $71.32, against a 52-week range of $42.53 to $72.77 and versus a consensus price target of $77.41 from Wall St. analysts. American Tower shares are down 2.1% at $77.33, against a 52-week range of $58.53 to $79.05 and a consensus rice target of $81.90 for the stock.

We did not see a call in Crown Castle International Corp. (NYSE: CCI), but its shares are down 1.6% at $73.90 in sympathy with the peer downgrades.

JON C. OGG