Apple's Core: The iPhone (Update 1)

NEW YORK (TheStreet) -- Apple(AAPL) reports second-quarter earnings after the bell Tuesday and investors will be paying particularly attention to iPhone sales, given recent worries of a slowdown.

The importance of the iPhone is vast, as it accounted for 52.66% of Apple's revenue in its most recent quarter.

Concerns about iPhone sales strengthened last week, when Apple supplier Qualcomm(QCOM) said it's seeing supply constraints for its 28 nanometer (NM) chips during its second-quarter earnings call. The San Diego-based chipmaker said it's working on getting supply up to speed, but that's led some to believe Apple may not sell as many iPhones as it could.

Canaccord Genuity analyst T. Michael Walkley lowered his near-term iPhone estimates, as iPhone 4S sales slow down in developed markets. He did raise fiscal 2012 iPhone estimates based on expected strong demand for the iPhone 5.

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"Our recent channel checks indicated iPhone sell-through share has modestly declined in certain developed markets, and we expect this could continue as Android competitors ramp new smartphones during the June and September quarters and consumers start to hold off iPhone purchases in anticipation of the iPhone 5," Walkley wrote in his research note. He lowered his 2012 earnings estimates but raised his 2013 earnings.

Walkley rated Apple shares buy and raised his price target to $740 from $710.

Apple sold 37.04 million iPhones, 15.43 million iPads, 5.2 million Macs, and 15.4 million iPods during its all important first-quarter, which Bill Kreher, technology analyst for Edward Jones, described as "mind-boggling."