Shares of Research In Motion Ltd., which have soared over the past two months on a burst of positive sentiment, fell sharply Friday as investors digested a fresh reason to worry about the smartphone maker.

After gaining momentum with the unveiling of its new BlackBerry 10 device, RIM released earnings on Thursday that contained worrying new details about the company's service revenue – a key source of much-needed income.

On a conference call with analysts Thursday, RIM management seemed unable to reassure investors worried about declines in RIM's service revenues. That, combined with bearish analyst notes Friday, send the shares down about 22 per cent in Toronto.

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RIM, which has struggled against Apple Inc. and Samsung Electronics Co. Ltd., hauls in roughly one-third of its revenues from wireless operators for BlackBerry access to RIM's proprietary, secure messaging network. This is usually a per-device fee that ranges from a couple of dollars per month up, depending on how important the carrier is to RIM's business.

As RIM's market influence has faded, the company gradually lost the ability to demand steep fees from carriers. Now, even as smaller competitors in the mobile device management field offer ways to securely transmit communications from various smartphones, RIM will begin offering "tiered" pricing for access to its network in a way that analysts fear will reduce a crucial source of revenue.

And RIM's service revenues are a significant source of cash: In the third quarter, services were 36 per cent of RIM's $2.7-billion revenues. In the second quarter, service fees added more than $1-billion to RIM's coffers – a sizable chunk to be at risk.

Kris Thompson at National Bank Financial, the analyst whose bullish note led to RIM's unexpected 17-per-cent surge on U.S. Thanksgiving in late November, led the bears on Friday by downgrading RIM shares.

In his previous note, Mr. Thompson had raised his price target from $12 to $15, capturing the positive sentiment around a company in the lead-up to the January 2013 launch of RIM's new BlackBerry 10 phones.

Friday morning, however, Mr. Thompson changed his mind: He downgraded the stock to "underperform" and slashed his price target from $15 to $10 on worries about RIM's service revenue.

Unique among handset makers, RIM always pulled in extra cash from its proprietary messaging network – and fresh news in Thursday's results reminded analysts of the risks to RIM's business model.

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"RIM reported decent overall results," Mr. Thompson wrote in his note. "Then management disclosed that monthly service revenue will undergo a change to a tiered menu. When peppered with questions, management was ill prepared to provide satisfactory answers. We believe investors will punish the stock until service revenue can be better quantified. We do not believe that RIM can sustain profitability with a standalone hardware business."

Mike Walkley, who follows big handset companies for Canaccord Genuity, reiterated his "sell" rating partially because the migration to the BlackBerry 10 platform – from RIM's current BlackBerry 7 software – "adversely impacts" service revenues. RIM beat Mr. Walkley's estimates for the third quarter, but he says his thesis remains unchanged.

"With our analysis indicating increasing competition from iPhone 5, Android and Windows 8 smartphones in Western markets … we expect softer sales of BB7 smartphones in future quarters with persistent pricing and margin pressure," Mr. Walkley said. "While RIM management remains bullish for its BB10 smartphone launch January 30, we do not believe BB10 devices will turn around its struggling business."

Still, some analysts saw much to admire in RIM's third quarter. The company's new CEO Thorsten Heins took hold of a struggling company that was missing product deadlines and has, to some extent, whipped it into fighting shape. Tom Astle of Byron Capital Markets noted RIM's strong balance sheet, a new product that is raising eyebrows, a "motivated" global network of wireless operator partners and a "loyal and long-suffering user base" around the world.

"RIM reported what we think was a very well-executed quarter," he wrote, adding, "for a company with an ancient product line."