* RIM CEO says service revenue not going away
* Analysts say new fee model may weigh on revenue, margins
* New BlackBerry 10 phones set to unveil in January
* Shares fall more than 20 percent following two-month rally (Updates to close)
By Allison Martell and Chandni Doulatramani
Dec 21 (Reuters) - Shares of BlackBerry maker Research In Motion Ltd plunged more than 20 percent on Friday on fears that a new fee structure for its high-margin services segment could put pressure on the business that has set the company apart from its competitors.
It was the stock's biggest, single-day, percentage price drop since September 2008. But shares were still nearly 80 percent above the year's low, which was reached in September. They started to rally in November as investors began to bet that RIM's long-awaited new BlackBerry 10 phones, which will be unveiled in January, would turn the company around.
The services segment has long been RIM's most profitable and accounts for about a third of total revenue. Some analysts said there was a risk that the fee changes could endanger its service ecosystem and leave the Canadian company as just another handset maker.
The fee changes, which RIM announced on Thursday after market close, overshadowed stronger-than-expected quarterly results. The company said the new pricing structure would be introduced with the BlackBerry 10 launch, expected on Jan. 30.
RIM said some subscribers would continue to pay for enhanced services such as advanced security. But under the new structure, some other services would account for less revenue, or even none at all.
Chief Executive Thorsten Heins tried to reassure investors in a television interview with CNBC on Friday, saying RIM's "service revenue isn't going away".
He added: "We're not stopping. We're not halting. We're transitioning."
Since taking over at RIM in January, Heins has focused on shrinking the company and getting it ready to introduce its new BB10 devices, which RIM says will help it claw back ground it has lost to competitors such as Apple Inc and Samsung Electronics.
But the new services pricing strategy came as a shock to markets, and some analysts cut their price targets on RIM stock.
RIM will not be able to sustain profitability by relying on its hardware business alone, said National Bank Financial analyst Kris Thompson, whom Thomson Reuters StarMine has rated the top RIM analyst based on the accuracy of his estimates of the company's earnings.
Thompson downgraded RIM's stock to "underperform" from "sector perform" and cut his price target to $10 from $15.
Forrester Research analyst Charles Golvin said the move was likely about stabilizing market share: "At the moment, they need to stem the bleeding."
He said the tiered pricing might line up better with RIM's subscriber base as it expands in emerging economies.
RIM's Nasdaq-listed shares closed down 22.7 percent at $10.91 on Friday. The stock fell 22.2 percent to C$10.86 on the Toronto Stock Exchange.
The success of the BB10 will be crucial to the future of RIM, which on Thursday posted its first-ever decline in total subscribers. Heins said on CNBC that the company expected to ship millions of the new devices.
He cautioned that this will require heavy investment, which will reduce RIM's cash position in its fourth and first quarters from $2.9 billion in its fiscal third quarter. He said, however, it would not go below $2 billion.
Still, doubts remain about whether RIM can pull off the transformation. Needham analyst Charlie Wolf said the BB10 would have to look meaningfully superior to its competitors for RIM to stage a comeback.
Canaccord Genuity analyst Michael Walkley said it was highly unlikely that the market would support RIM's new mobile computing ecosystem, and he remained skeptical about the company's ability to survive on its own.
"We believe RIM will eventually need to sell the company," said Walkley, who cut his price target on RIM shares to $9 from $10.
Baird Equity Research analysts said BB10 faced a daunting uphill battle against products from Apple, as well as those using Google Inc's Android operating system, and, increasingly, phones with Microsoft Corp's Windows 8 operating system.
Baird maintained its "underperform" rating on the stock, while Paradigm Capital downgraded the shares to "hold" from "buy" on uncertainty around the services revenue model.
"RIM has gone from having one major aspect of uncertainty - BlackBerry 10 adoption - to two, given an uncertain floor on services revenue," William Blair analyst Anil Doradla said.
RIM will have to discount BB10 devices significantly to maintain demand, Bernstein analyst Pierre Ferragu said.
The BlackBerry, however, still offers the security features that helped it build its reputation with big business and government, a selling point with some key customers.
Credit Suisse maintained its "neutral" rating on the stock, but not because it expected BB10 to be a big success.
"Only the potential for an outright sale of the company or a breakup keeps us at a neutral," Credit Suisse analysts said.
Separately on Friday, ailing Finnish mobile phone maker Nokia said it had settled its patent dispute with RIM in return for payments. Nokia did not disclose detailed terms, but said the deal included a one-time payment to be booked in the fourth quarter, as well as ongoing fees, all to be paid by RIM.
$1=$0.98 Canadian Reporting by Chandni Doulatramani in Bangalore and Allison Martell in Toronto. Additional reporting by Sinead Carew in New York; Editing by Ted Kerr, Dale Hudson, Janet Guttsman,; Lisa Von Ahn, Peter Galloway and Leslie Gevirtz