BlackBerry Ltd Chief Executive John Chen fired a salvo at T-Mobile US Inc on Tuesday, calling ill-conceived a promotion run by the company that encourages customers using BlackBerry smartphones to upgrade to iPhones. T-Mobile US, which is majority owned by Deutsche Telekom AG, sent out emails to some of its customers last week, pitching free iPhone 5s and touting the promotion as a, great offer for BlackBerry customers. That sparked a brouhaha in social media forums after some of the telecommunications companys loyal BlackBerry customers reacted angrily to the offer, which they perceived as a slight. The backlash prompted T-Mobile US Chief Executive John Legere to respond publicly.