Shares of Sprint Nextel Corp. have been falling in recent times, even as the US' third-largest mobile operator faces bankruptcy after the expensive acquisition of sole rights to Apple's iPhone's services last fall.

Stock fell 4.33 percent or 13 cents, on NYSE, as of 11.39 am ET on 19 March, according to Bernstein Research analyst Craig Moffett's financial report.

"To be clear, we are not predicting a Sprint bankruptcy," Moffett was quoted as saying by Forbes in the research note. "We are merely acknowledging that it is a very legitimate risk. And notwithstanding a recent rally in Sprint shares, we believe that risk is rising," he clarifies.

The company faces a financial debt crisis, following its inability to provide bandwidth for the iPad's 4G network. As a result, Sprint's network services run at much slower speeds than the proposed 4G.

To add to its woes, the release of the anticipated 4G LTE-enabled iPhone later this year could pave the way for more debts and bandwidth issues. Besides, rival network services are already switching over to 4G services.

The company faces "increased competition, growing debt and steep costs, with flops in Clearwire's WiMAX technology, a failed LightSquared partnership and a risky $15.5bn gamble on Apple's iPhone further complicating its position," reports Moffett.

However, Pacific Crest analyst Steve Clement has a more optimistic view.

"The risk they could go bankrupt has gone up but that's a very very low risk," Clement writes.

Sprint is reportedly committed to buying a minimum of 24 million iPhones inside the next few years, owing to contractual obligations with Apple. According to appadvice, the net worth of the deal is in the region of $15.5bn. This is slightly better than the news, which came out in October that the company was committed to purchasing 30.5 million iPhones over the next four years just to remain competitive.

Moffett also notes that Sprint's debt maturities through 2013 are covered and its debt due the next year are modest, according to Dow Jones Newswires on Wall Street Journal.

"But thereafter the company faces a sustained multiyear barrage of large maturities that will need to be addressed," Moffett concludes.