Research in Motion, the maker of the BlackBerry smartphone, did a layoff at its U.S. headquarters in Irving Wednesday, a source familiar with the situation said. The source, who requested anonymity because of the sensitivity of the matter, confirmed that a majority of those affected were call-center staffers. There was speculation that approximately 200 staffers were let go, although the source could not confirm a number. RIM employs in the ballpark of 700 people in Irving, the source said. In an emailed statement, a RIM spokesman declined to comment on the layoff. The company is reducing its global workforce by...