Sprint Nextel
Sprint Nextel
Fortune 500 rank: 90
2011 loss: $2.9 billion
A fickle subscriber base and a hyper-competitive market took a toll on the nation's third-biggest mobile service provider in 2011. At year-end, Sprint Nextel posted big annual losses, marking the fifth consecutive year it lost money.

There were some signs of hope with the launch of Apple's wildly popular iPhone 4 and iPhone 4S in the further quarter. The day Sprint stores started carrying the phones, they produced the best day of sales of any device family in the company history. That quarter the company sold 1.8 million iPhones -- 40% of them to new subscribers.

That didn't translate into big profits, however. Sprint sells the phones at a loss to drive subscriptions. And despite a 40% increase in subsidy expenses to cover loss-leader expenses, Sprint still sold fewer iPhones than its two larger rivals, Verizon and AT&T. On the bright side, analysts say iPhone sales could reduce some of the high subscriber turnover that has plagued the carrier.

By Anne VanderMey, reporter - Last updated May 08 2012: 1:42 PM ET