iPhone sales dip in North America: Bad news for AT&T?

Apple(s aapl) set a record of 51 million iPhone sales in Q4, largely due to its success in the emerging markets with the introduction of the cheaper iPhone 5c. But what worked in the rest of the world didn’t work back in the U.S. and Canada.

In Apple’s earning call on Monday, CEO Tim Cook said iPhone shipments and revenues dipped slightly in North America as Apple had trouble keeping up with demand. While the 5c may have proved popular in emerging markets, it wasn’t much of hit among U.S. consumers. To them, the $100 difference in price didn’t seem worth it to trade down from the 5s to the 5c.

iPhone 5c

The bulk of North American sales are in the U.S., so any hit taken on iPhone sales is bound to affect the U.S. carriers. Verizon Wireless(s vz)(s vod) so far is the only one of the four nationwide operators to report Q4 earnings, and suspiciously it failed to break out iPhone activations for the first time since carrying the device. Still, Verizon had 1.7 million net additions for the quarter, so its overall results weren’t impacted much by Apple.

AT&T(s t), however, is much more exposed to the iPhone than its arch competitor. Not only was it Apple’s first carrier partner for the iPhone, Ma Bell has routinely done a much bigger business in iPhone sales and activations than any other carrier since the smartphone’s introduction across the market. In Q4 of 2012, AT&T(s t) activated 8.6 million iPhones compared to Verizon’s 6.2 million.

AT&T was already under pressure in the last quarter, taking the major brunt of T-Mobile’s(s tmus) Un-carrier attacks on the U.S. mobile industry (a strategy that brand researcher YouGov found is working). A hit to its bread-and-butter iPhone business, would add insult to injury. In any case, we’ll find out this afternoon when AT&T posts its Q4 results.