Shares of Redback Networks Inc. face an uncertain Thursday after investors decided yesterday's earnings call wasn't all that good.

Redback stock was up 5 percent in early after-hours trading after the company reported first-quarter earnings. But during a conference call with analysts, investors did a 180, erasing the gains and eventually sending the shares down 6 cents (0.3%) from their closing, to $24.15.

It seems there's always some drama with Redback. The stock made an opposite U-turn after an earnings call six months ago. And in January, when the company reported its return to profitability, the earnings report was delayed, setting investors' nerves on edge. (See Wild Ride for Redback Shares.)

The news certainly seemed good at first, as Redback reported a pro forma profit of $4 million, or 5 cents per share, beating analysts' consensus forecast of 3 cents, according to Reuters Research .

But the company was in the red when measured by generally accepted accounting principles (GAAP), and while analysts had expected that, the GAAP numbers were a bit worse than predicted.

For its first quarter, which ended March 31, Redback reported GAAP losses of 2.6 million, or 5 cents per share, on revenues of $57.9 million, compared with profits of $310,000, or 1 cent per share, on revenues of $48 million the previous quarter. (See Redback Reports Q1.) Analysts had expected a GAAP loss of 3 cents per share.

For its first quarter a year ago, Redback announced losses of $2.9 million, or 5 cents per share, on revenues of $34.3 million.

Getting back to that stock price, though -- none of these numbers are exactly secret, so perhaps it was the tone of the conference call with analysts that soured the mood of investors.

"We expect to have significant revenue driven by several large customers. Therefore, because of the timing of these revenues, our actual quarterly results may vary up and down," CFO Thomas Cronan told analysts on last night's call. That "up and down" part -- especially the "down" -- often doesn't sit well with investors. (See Extreme Slump Continues.)

Still, Redback painted a bright picture of its overall future. Its book-to-bill ratio was "significantly greater than 1" for the quarter, CEO Kevin DeNuccio said on the call. That's an indication that Redback's revenues could grow further.

In fact, Redback said revenues could climb 10 percent in the second quarter. That would mean revenues of about $63.7 million, outpacing analysts's forecast of $56.7 million.

It's worth noting that Redback's share price has quintupled in the past 12 months. Redback is being driven by a number of big-ticket buildouts with customers like BellSouth Corp. (NYSE: BLS). (See How Redback Won BellSouth.)

During the call, Redback 'fessed up to having won more work with Orange (NYSE: FTE), which was a customer of Redback's older SMS platform. Redback is involved with two networks there: a next-generation broadband edge buildout that includes Redback's flagship SmartEdge product line, and an edge network built for VOIP.

France Telecom was one of Redback's top five customers during the quarter, as were all three U.S. RBOCs, DeNuccio said. He added that Redback doesn't consider itseslf to be shut out of any major RBOC upgrades -- good news if it's true, because some have worried whether Redback's BellSouth deal can stand up to that company's acquisition by AT&T Inc. (NYSE: T). (See Will AT&T Value BellSouth's Vendors?.)

In its North American sales, Redback is "getting diversified from the big BellSouth buildout we've been doing for the past couple of quarters," DeNuccio said.

— Craig Matsumoto, Senior Editor, Light Reading