In about five hours, Apple will be reporting their earnings for the second quarter of the 2012 fiscal year. Already, though, analysts are starting to speculate about what this quarter’s report will bring, and some of the speculation has investors worried. In January, Apple reported a record quarter with $46.33 billion in revenue.

The company also reported 5.2 million Macs sold, along with 15.43 million iPads. Both impressive numbers, but what really pushed Apple over the top was iPhone sales: in the first quarter of the 2012 fiscal year (October-December 2011), Apple sold a staggering 37.04 million iPhones. In fact, of that $46.33 million in revenue, the iPhone accounted for over half of Apple’s revenue (and more revenue that all of Microsoft generated in the same quarter).

Unfortunately for Apple – worryingly for investors and analysts – it’s not likely that Apple has sold nearly as many iPhones in the second quarter as they did in the first. After all, last quarter kicked off with the launch of the overdue iPhone 4S, which hit stores in October and was a huge hit. Especially worrisome is data released this morning as part of AT&T’s first quarter earnings report. According to their data, iPhone activations were down an alarming 3.3 billion activations lower than those of the previous quarter. While the fourth quarter of 2011 (October-December) saw 7.6 billion activations, in the first quarter of 2012 activations tumbled to 4.3 billion. While that’s still higher than any of the first three quarters of 2011, it’s still pretty alarming.

That said, there are some important things in both AT&T’s and Verizon’s earnings data that is encouraging. On both carriers, the iPhone appears to be beating Android. AT&T’s report says that 78% of all smartphone activations were iPhones – 4.3 million out of 5.5 million smartphone sales. Meanwhile, last week Verizon’s own quarterly earnings data showed that the iPhone accounted for 3.2 million of their 6.3 million smartphone sales. In other words, though the iPhone may not be selling as well as investors had hoped, it still is selling far better than pretty much any other smartphone out there.

Nevertheless, investors and analysts are worried. Apple’s stock has taken quite a nosedive today following AT&T’s earnings report, falling to $561 per share after hovering near $600 for several weeks.

While analysts have accounted for a decline in iPhone sales for the second quarter, the worry remains that Apple will not manage to meet even the lowered expectations. According to Piper Jaffray analyst Gene Munster, Apple is expected to have sold 31-32 million iPhones for the quarter. If Apple doesn’t meet those numbers, it could mean pretty big trouble for Apple. Of course, analysts like Munster have also predicted drops in iPad and Mac sales for this quarter as well. While Mac sales may well be down again, it seems likely that iPad sales will increase. Estimates for iPad sales are around 12-13 million units. The new iPad, however, sold 3 million units in just four days following its launch. Though the launch was late in the quarter, it seems likely that first quarter iPad sales will see an increase.

Yet, even assuming the iPad meets or exceeds estimates, there’s a chance Apple could still fall short. The iPhone is a major driver of Apple’s revenues, and if sales should fall short of estimates, then Apple’s revenue will almost certainly do the same, which could have a significant impact on the company’s stock.

Despite the stock hit, though, some analysts remain optimistic. Erica Ogg of GigaOm predicts that iPad sales will be “a highlight” and give the company “a nice boost.” Meanwhile, ZDNet expects iPhone sales to top 33 million iPhones and iPad sales to exceed most estimates.

While nothing will be known for certain until Apple released the numbers after the markets close this afternoon, it seems a pretty safe bet that Apple will be in good shape for this quarter. While we probably shouldn’t expect the record-setting numbers of the previous quarter, look for Apple to meet or exceed most expectations, and for the company’s stock to rebound when trading re-opens tomorrow.