Apple set mobile-device sales records in the first quarter of 2012 by expanding its global iPhone shipments 88 percent year-over-year to 35.1 million units and boosting iPad shipments by 151 percent to 11.8 million units.

Apple also outgrew the PC market overall by increasing its quarterly Mac desktop and portable shipments by 7 percent year-over-year to 4 million units.

After Verizon Wireless reported lower than expected iPhone activation numbers last week, investments firms reduced their first-quarter iPhone shipment estimates to the range of 31 million to 33 million units. According to Apple executives, however, the iPhone experienced strong sales growth in the Asia Pacific and Japan markets -- where sales more than doubled year-over-year.

First-quarter iPhone sales in Greater China, for example, were driven by huge demand following the January launch of the iPhone 4S and China Telecom's debut as an iPhone carrier in March.

"On a macro basis, China has an enormous number of people moving into the higher income groups -- the middle class, if you will -- and this is creating a demand for goods, not just Apple's but other companies' goods as well," Apple CEO Tim Cook told investors Tuesday. "There's a tremendous opportunity for companies that understand China, and we're doing everything we can to understand it and serve the market."

Huge U.S. Upgrade Opportunity

Piper Jaffray said that Apple's record iPhone sales are proof that the iconic device maker's international growth is only just beginning.

"Apple's March quarter results are particularly important as they are evidence that the company's growth story can be successful in these emerging markets," said Piper Jaffray analysts Gene Munster and Douglas Clinton.

Nevertheless, the U.S. market continues to represent a huge iPhone sales growth opportunity for Apple and its carrier partners.

"The bigger story for iPhone is the coming launch of iPhone 5, which we expect in October 2012," Munster and Clinton wrote in a Tuesday investor note.

Among other things, the iPhone's combined smartphone share at AT&T and Verizon amounted to 64 percent in March. "We believe that number could climb to 80 percent in the next year," Piper Jaffray's analysts said.

According to the investment firm's survey work, 94 percent of existing iPhone owners in the U.S. expect their next phone will be an iPhone. Assuming an average iPhone life of 21 months and an iPhone user upgrade level of 85 percent implies that "45 percent of [Apple's future iPhone sales] through 2015 are 'in the bag,' " said Munster and Clinton.

New iPad Supply Constrained

Apple's iPad sales more than doubled in each of the company's regional sales segments. Helping to drive the company's record first-quarter tablet growth were more than 200,000 apps specifically designed for iPad in the iTunes App Store, and the company's new $399 price for its prior-generation iPad 2.

"From what we are seeing, [the lower entry iPad price] unlocks some education demand that is probably a more price-sensitive customer," Cook said. "Also, in several other countries, there was a marked change in demand at that price point."

Still, Cook said, the release of a new iPad model was the biggest contributing factor to its shipment growth.

"We're still supply-constrained on the new iPad [because] we're selling them as fast as we can make them," Cook told investors.

Gartner, Forrester and IDC are forecasting 330 million to 375 million media tablet sales in 2015. Unit shipments in the global tablet market are on track to achieve parity with the global PC market within the next three years.

"Our view is that the tablet market is huge, and we've said that since Day One," Cook said.