With Apple’s earning release for the past quarter that ended two weeks ago now just eight days away, analysts are running their spreadsheets like crazy, falling over themselves to guesstimate just how many iPhones the company sold.

And as the iPhone lineup accounts for more than half of Apple’s revenue, no wonder it’s become Apple’s most important business metric. AAPL passing the $600 milestone also owes much to the success of the iPhone, as does the company’s projected $1 trillion valuation.

It’s almost as if Apple’s future and fortunes depend solely on the iPhone. With that in mind, seasoned watchers should ask themselves whether Apple can retain its crown of the world’s top smartphone maker in the March quarter.

And, is the six-month old iPhone 4S still attractive enough to keep people interested until the fabled iPhone 5 (or whatever it ends up being called) arrives later this year? As always, only time will tell. But one thing is certain: Wall Street has high hopes in Apple’s ability to keep the iPhone freight train chugging along…

According to Philip Elmer-DeWitt over at the Fortune blog, the estimates range from 26 to 44 million iPhone units, with the best analysts’ consensus of 35 million units.

Man, I should have been an analyst!

Note that these projections are based on a poll of 48 professional and independent analysts.

The author writes:

The average among the Wall Street analysts is 30.5 million, which would represent a year-over-year unit sales increase of 63.8%. […] To hedge our bets, we’ve singled out the six analysts who have turned in the most accurate estimates over the past five quarters. Their consensus: nearly 35.1 million units, an increase of 88.5% year over year.

Apple is scheduled to report its fiscal 2012 second quarter earnings next Tuesday, April 24. We will be covering the earnings release and a conference call with analysts live, bringing you the latest tidbits as they hit the wires.

So, what happens if quarterly iPhone sales cause a dip in revenue? Well, there’s always iPad 3, according to Zack Whittaker over at ZDNet:

In theory, the numbers balance each other out. But it’s more likely that more people are still buying the entry-level 16GB iPhone at $199 on contracts rather than going all-out on an unlocked device, costing consumers a greater price tag of $649.

Compare this to the iPad 3, however, its entry level tablet at $499 could generate more revenue per device than the entry-level iPhone does. Plus, while its predecessor the iPhone 4, and the now ageing iPhone 3GS remains on sale, Apple is taking to increase the surface area its smartphone has by having three vastly different iPhones on sale.

Some analysts are calling for a monster iPad quarter with an estimated sales of twelve million units, a 156 percent growth.

Whichever way you look at it, it should be interesting seeing if Apple ships enough handsets to retain its title of the world’s top smartphone maker. Remember, Apple briefly lost the #1 slot to Samsung in the September 2011 quarter.

Apple is also entering a sensitive seasonal decline as iPhone sales tend to stay flat in the June quarter and then fall off the cliff in the September quarter because consumers will be holding off their purchase in anticipation of a new model.

Usually, people abandoning their BlackBerries tend to pick an iPhone. As Research In Motion continuous on a downward spiral, Apple should be able to keep and hopefully grow iPhone sales until a sixth-generation iPhone launches, either this summer or – more probably – sometime in Fall.

What’s up with Apple’s shares losing more than six percent of their value last week, knocking $36 billion off the company’s market cap?

Don’t worry, this is normal. Jason Schwarz calls it the Apple slingshot effect and shorts are loving it:

If you can keep a good stock down then you are able to load up for the ride back up. It’s like a slingshot – the harder you pull, the more propulsion you generate.

What’s your take, how many iPhones did Apple sell in the past quarter? Are they going to beat the 37 million iPhone shipments reported for the holiday quarter?

Play an analyst down in the comments.