Shares of Research in Motion Ltd. fell on Friday, falling more than 2.8 percent after a report that the it will push back the release of its 3G BlackBerry phone for AT&T to as late as August.

People close to the companies say AT&T has concerns about the phone's call quality, Fortune magazine said on its web site.

The delay could also impact RIM phone shipments and subscriber growth for the second fiscal quarter ending August 30.

In February RIM CEO Jim Balsilie said the company would introduce devices based on the high-speed technology standard HSDPA which is popular in Europe and is being used by AT&T in the U.S.

AT&T's chief executive said last year that a high-speed version of the Apple iPhone would be introduced some time in 2008.