Shares of Nokia were sent reeling Friday after the No. 1 mobile phone maker warned that its market share will fall in the third quarter.

Nokia shares tumbled $2.37, or 10.6 percent to $19.94 in late-morning trading. The stocks of rival wireless equipment makers Motorola, Ericsson and Qualcomm tumbled in sympathy.

In a regulatory filing, Nokia forecast an erosion in its mobile-device market share in the third quarter. That contrasts with previous projections in July when the company said it expected market share to hold steady versus the second quarter.

Nokia attributed the lower market share to a “tactical decision” to not match “aggressive” pricing of some competitors and the slower-than-expected of a mid-range handset.

“Nokia's strategy is to take market share only when the company believes it to be sustainably profitable in the longer term,” the company said. “Nokia has not broadly participated in the recent aggressive pricing activity - as it believes that the negative impact to profitability would outweigh any short term incremental benefits to device unit sales.”

At the same time, the Espoo, Finland, company, which will report third quarter earnings on October 16, said it expects to increase its market share for calendar 2008 overall.

In the second quarter, Nokia had 39.5 percent share worldwide, according to Gartner, followed by Samsung with 15.2 percent and Motorola with 10 percent.

On Friday, shares of: Motorola slid $.20, or 2.2 percent, to $8.94, Qualcomm fell $1.40, or 2.9 percent to $47.14 and Ericsson slipped $.40, or 3.8 percent to $10.13.