Dish Network has boosted its bid for Clearwire to $4.40 per share, 29 percent above Sprint Nextel's most recent offer, and said it is prepared to buy up the stock of a minority of shareholders. In a letter sent Wednesday to Clearwire Chairman John Stanton, Dish said its board had approved the offer and it was prepared to execute the deal. On Friday, Clearwire plans to hold a special shareholder meeting to consider Sprint's offer to buy out the roughly half of the company that it doesn't already own.