Sprint (S) and Nextel
The potential: In 2005, Sprint paid a whopping $36 billion for a majority stake in fellow telecom company Nextel to boost its user base and revenues and create a wireless powerhouse. At least that was the idea.
Why it failed: Both companies thought they would be able to quickly merge customers and catch up to Verizon (VZ) and AT&T. But cultural clashes and incompatible wireless technologies made that impossible. Nextel executives began leaving soonafter the merger. Throughout 2008 and 2009 there were billion dollar losses, thousands of layoffs and the company's stock plummeted.