analyst craig moffett says the nation's third largest wireless carrier is spending heavily to upgrade its wireless network. he thinks the upgrade cost, along with signs the yet-to-be- unveiled iphone 5 will require a wireless technology sprint is only beginning to build will weigh heavily on the company, raising what he calls a legitimate risk of bankruptcy. >> the proximity of the iphone 5. now that we've seen the ipad. it confirms that the ipad has l.t.e. functionality if there was any doubt that the iphone was going to have l.t.e. functionality that's essentially gone now and unfortunately that just disadvantages a sprint that is already in a very precarious position. >> tom: shares of sprint ended the session down 4.5%. insurance on sprint bonds is pricing in a 50-50 probability of bankruptcy in the next five years. moffett doesn't see an imminent risk of bankruptcy, but he cautions the carrier's i.o.u. pressures start to mount in 2015. >> as tempting as it would be to say that sprint may have found a bottom. this is a very, very risky stock and probably not an appropriate investm