The momentum is shifting for American Tower.American Tower (AMT -1.19%) has hit a speed bump in recent years. The communication infrastructure operator's adjusted funds from operations (FFO) slowed considerably last year, rising only 2.1% for the full year after growing at a double-digit pace for years. As a result, the company's dividend growth rate has also slowed, from a 10% annualized rate at the end of last year to 3.2% annualized in the second quarter. That slowdown has weighed heavily on its shares, ...