Sprint Nextel made a net loss of $1.6 billion for the second quarter, swollen by the cost of shutting down its Nextel wireless network, but the company is more optimistic about future profitability. The net loss was 16 percent higher than the $1.37 billion reported a year earlier, and included a $430 million charge for accelerated depreciation of Nextel network assets, and $623 million of other charges related to the network shutdown. Revenue totalled $8.88 billion, almost unchanged from a year earlier.