(Telecompaper) BlackBerry co-founders Mike Lazaridis and Doug Fregin are considering a joint bid to acquire the smartphone maker. They disclosed an 8 percent stake in the company in a SEC filing and said they have hired bank advisers to consider a full takeover of the group. BlackBerry agreed last month to a takeover by its largest shareholder Fairfax Financial for USD 4.7 billion. Fairfax holds around 10 percent in the company. However, the Fairfax bid still depends on due diligence and a final agreement. Goldman Sachs and Centerview Partners are advising the BlackBerry co-founders on their potential bid. Lazaridis was earlier reported to be in talks with private equity groups about mounting a takeover offer. He served as co-CEO of BlackBerry until early 2012 and stepped down from the company's board in May 2013.