Blackberry Earnings to Reveal First Glimpse of Z10 Sales

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This is where reality sets in.

BlackBerry will report its fiscal fourth quarter numbers Thursday morning. Analysts are looking for a loss per share of 31 cents on revenue of $2.8 billion.

A few major forces are at play.

First, BlackBerry had about a month's worth of sales of the Z10 in the U.K. and Canada, two major markets where demand looked strong.

Second, BlackBerry may have seen weaker sales of its bread-and-butter BlackBerry 7 devices, as customers waited to see the Z10.

And lastly, BlackBerry lost one million subscribers last quarter. Will it lose the same number this time? Or perhaps even more?

Blackberry Stock a 'Buy'?

In addition to these three variables, analysts are counting on the stock to be volatile because nearly one-third of the available shares were held by short sellers at the end of February.

(Read More: BlackBerry Targeted by Short Sellers as Market Awaits Results )

The integrity of BlackBerry's turnaround story is at stake. The stock is up more than 20 percent since the beginning of the year on hopes that the BlackBerry Z10 and the BlackBerry 10 software behind it will reverse the company's foundering fortunes.

The U.K. and Canada Z10 launches supported the storyline — some U.K. stores reported stock-outs of the white version -- but the U.S. launch was less impressive. Goldman Sachs said earlier this week that several of the stores they surveyed were selling fewer than 10 units per day.

(Read More: Investors Abandon Blackberry After 'Disappointing' Launch )

But in the near-term, the most important number in the report is probably the subscriber number. "BlackBerry subscribers" are phone owners who use BlackBerry's secure network, mostly for messaging.

In the past, carriers have been willing to pay BlackBerry for access to its network, but with BlackBerry 10 devices, that model— and the high-margin service revenue that comes with it — is changing. Add to that the fact that BlackBerry's installed base is shrinking as former users switch to Apple iPhone and Android devices, and there are a lot of questions about how well the company will be able to defend its valuable subscriber base.

We'll start to get a better sense of it early Thursday — BlackBerry's numbers are due out at 7 a.m.