Companies always refer to themselves as leaders especially in press releases. It’s generally a meaningless term unless of course its Gartner calling the company a Leader in the context of a Magic Quadrant.
Mitel was recently recognized as such in the Gartner Magic Quadrant for UC 2014. Eleven companies were included in the report, and four were recognized as Leaders (Microsoft, Cisco, Avaya, and Mitel). I think this is a first time for Mitel, so congratulations are in order.