Research In Motion Ltd. Said Wednesday it expects fourth-quarter revenue to be at or near the midpoint of its previously forecasted range, in spite of reporting a 20 percent growth in subscribers in December.

The BlackBerry maker said that based on a series of factors -- including product mix, lower inventory levels and a higher ratio of new subscriber sales to upgrade and replacement sales -- caused a spike in subscriptions to outperform revenue and earnings performance in the holiday quarter.

However, investors were unimpressed as RIM also said revenue would be in the middle of its forecast while margins and earnings would come in at the low end of prior views.

The BlackBerry maker said in December it expected fourth-quarter revenue of $3.3 billion to $3.5 billion, with earnings in the range of 83 cents to 91 cents a share. It had previously expected gross margin of 40 to 41 percent.

RIM said it now expects net subscriber account additions in the quarter that ended February 28, to be 20 percent higher than the 2.9 million additions it forecast on December 18.

RIM achieved a very strong start to the holiday buying season and the momentum carried on stronger than expected during the past seven weeks despite a seasonally slower timeframe and the challenging economic environment, said Co- Chief Executive Jim Balsillie.

Although nearly 500,000 Storms sold in the month after its Nov. 21 launch, was lower compared to the 2.4 million iPhone 3G devices sold by AT&T Corp. and Apple Inc. in that device's first full quarter on the market. The Storm phone is available through Verizon Wireless.

RIM is set to release its fiscal fourth-quarter results on April 2.