Just how many people are willing to shell out hundreds of dollars for an Apple (AAPL) - Get Report iPhone? That's the question on the minds of investors after the tech giant's iPhone sales slid during its fiscal second quarter.

"They're running out of people to sell premium products to," said Michael Ingram, a market analyst with BGC Partners in London.

The company still sold 51.19 iPhones during its fiscal second quarter, a tad higher than expectations. This is still about 10 million less than the same quarter last year, sparking a selloff in Apple shares following its earnings report, which was released on Tuesday after the markets closed. The 18% year-over-year drop in iPhone sales dinged overall revenue, causing the company to post its first quarterly decline in sales since 2003.

"The problem is, this stock has become so iconic for growth investors, that even a break after 51 quarters of continuous growth is taken very badly," he said. "This appears not to be just a blip, but at the very least a serious stumble. The company's own guidance suggests that analysts need to take the red pen out again for their numbers."

Apple now expects fiscal third-quarter revenue between $41 billion and $43 billion, falling short of the $47.3 billion analysts had expected.

TheStreet's Jim Cramer, however, is looking to the longer term, considering Apple to be a "value play." Cramer, who holds Apple as part of his Action Alerts PLUS portfolio, and Research Director Jack Mohr noted investors have "increasingly shifted from long-term fundamental investing to short-term, event-driven trading, with the event being March- and June-quarter iPhone unit sales."

So while AAP is holding the stock for the long term, they said "the long term is irrelevant for the time being as the focus is exclusively on whether or not [Apple will] hit their next-quarter targets/sell-side forecasts."

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That's why many investors are worried the company's best days are over. "We need to see a significant product refresh before analysts can be confident that the growth momentum that we had seen until this point can be maintained," Ingram said.

Amid the slump in its hardware products, Apple touted its 20% year-over-year increase in services revenue. "We are very happy with the continued strong growth in revenue from Services, thanks to the incredible strength of the Apple ecosystem and our growing base of over one billion active devices," said Apple's CEO Tim Cook in a statement.