Here's the Real Reason Investors Should Be Worried About Apple's iPhone 5

"Verizon's margin for full year 2012 will be something like 46.8%, or perhaps a bit lower. In 2010, Verizon's margin was... 47.0%. They're actually flat over the timeframe the margin expansion thesis gained popularity," writes Moffett. "For the foreseeable future, however, margin volatility rules...and that dictates that the sloppy margins the industry will surely post in Q4 must not be ignored," the analyst adds.

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Other analysts across the telecom sector have slowly been cutting at their earnings expectations for Verizon an AT&T heading into the fourth quarter.

In an early December research note, bullish comments made by AT&T about overall quarterly smartphone sales caused Guggenheim Partners analyst Shing Yin to cut fourth-quarter earnings and margin forecasts for the carrier.

Given an estimate of 10 million smartphone sales in the fourth quarter - 80% of which Yin calculates are iPhones -- the analyst now sees wireless EBITDA margins at 31% for the quarter, bringing overall margins at or below 40% for the year.

"We believe 2012 upgrade rates had benefited from a one-time impact related to upgrade policy changes made in early 2011. Now that this one-time impact has passed, we expect upgrade rates, and subsidy expense, to be higher in 2013," wrote Yin, in a December 6 note to clients that followed comments made by AT&T's head of wireless.

That insight into what the analyst calls the "basic principles of smartphonomics" caused Yin to cut AT&T's price target from $35 per share to $33. Yin made a similar downward revision following Verizon's January disclosures on smartphone sales and subscriber growth.

The potential deterioration in wireless margins for growing industry players comes at a time when the likes of Sprint, the industry's number three player, are investing billions to grow out wireless networks and take on smartphone users. So far, however, efforts to handle the iPhone and slow-moving network upgrades have led to subscriber losses that raise more questions then they answer

For investors growing tired of the tick-by-tick hysteria surrounding Apple's value and shares, a focus on the iPhone's impact on overall telecom carrier profits may prove to be a far more revealing exercise.

Watch wireless margins to either provide a wrench in the profitability story of telecom giants, or to quiet skeptics once and for all.