Samsung’s falling stock price over the past month – down over 14% – was just the latest example of a smartphone maker to see its once high-flying shares tumble. It may be the last of the majors to tank but its decline marks the beginning of a new era of slower gains for smartphone stocks.

Apple’s (AAPL) stock price famously peaked last September and has since lost more than 40%. HTC’s price more than tripled from 2010 to an April 2011 peak but has fallen 80% since.

The days of hyper-growth, with millions of people a month buying their first smartphones, are nearly over. Repeat customers tend to wait two years or more before upgrading, leaving phone makers fighting for market share amid slower growth.

In most developed countries, more than half of mobile phone subscribers already have a smartphone. And in less-penetrated regions, consumers can’t afford to pay nearly as much for phones, pressuring profit margins.

The market doesn't wait

The stats say it may be another year or two until the point of total saturation hits. But as Federal Reserve chairman Ben Bernanke found out the hard way, the stock market doesn’t wait for future trends to hit, it anticipates them.

In the United States, 59% of phone users have smartphones already, according to the latest figures from comScore. That will reach 80% in about a year and 100%, if current trends hold, in 2015, according to mobile market analyst Horace Dediu.

Smartphone ownership rates are also already well over 50% in other developed economies such as Germany, France, the UK and Canada, according to comScore.

Already growth in shipments of new smartphones in the U.S. market dropped to 14% last year from 51% in 2011 and 52% in 2010, according to figures from IDC. Worldwide, growth slipped to 46% from 76% in 2010.

Remaining opportunities

Many of the remaining opportunities worldwide are in less-wealthy regions, countries such as China and India, where consumers can’t shell out $600 for a new phone and carriers can’t afford the massive subsidies common in the U.S.

That means cheaper phones, likely with lower profit margins as well. The average selling price of smartphones worldwide has already declined to $372 this year from $443 in 2011, according to IDC. That average is projected to slip to $309 by 2017.

The slippage is a combination of the fact that phones in developing countries on average sell for about two-thirds the price of phones in developed economies, and that average phone prices are falling 3% to 4% a year in all regions, IDC says.

Even table-pounding Apple bulls concede the smartphone market has entered a new phase. Raymond James analysts upped Apple from “outperform” to “strong buy” on Monday, citing its low valuation compared to other tech companies. As far as drivers for future revenue growth for Apple, though, the analysts were left pointing to opportunities in cars, televisions and possibly watches. Sales of the iPhone, currently Apple’s biggest revenue and profit generator, will be buffeted by “relatively small movements in customer upgrade rates, currency movements, commodity price changes, timing of new product launches, etc.,” the analysts warned.