Sprint Nextel is considering a sale of the Nextel wireless network it bought in 2005, but may have trouble finding a buyer for an asset whose value has plunged about 80 percent to an estimated $5 billion.

Sprint has struggled to integrate Nextel’s iDen network, used by public safety and construction workers, with its own services and has lost millions of customers since paying about $35 billion for Nextel Communications three years ago.