Research In Motion said its fourth-quarter earnings and gross margin would be at the low end of its previous forecast range, even as subscriber additions topped expectations, sending shares down 8%.

The BlackBerry device maker said on Wednesday that a variety of factors, including product mix, lower inventory levels and a higher ratio of new subscriber sales to upgrade and replacement sales, resulted in subscriber growth outperforming revenue and earnings performance in the holiday quarter.

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

But earnings per share and gross margin would be at the low end of its forecast range, and revenue would be at or near the mid-point, said the company, whose BlackBerry phones compete with Apple Inc's iPhone and other smartphones.

In December, RIM had forecast quarterly revenue between $3.3 billion and $3.5 billion, with earnings per share of 83 cents to 91 cents. Both were above Wall Street's estimates at the time, and analysts ratcheted up their forecasts and the stock surged, gaining more than 40% year to date.

Wednesday's outlook signals RIM could miss the mean analyst forecast for earnings per share of 86 cents, according to Reuters Estimates. Analysts were, on average, expecting revenue of $3.4 billion.

The U.S. shares of RIM fell to $52.50 in pre-market trading from their Nasdaq close on Tuesday of $57.038.