It issued a £3.5bn note secured by a portion of its investment in the US government's wireless spectrum infrastructure. Sprint has provided around $16bn of that investment as security for its bond, and used the proceeds to pay off debt.
To continue to use spectrum it will lease it from the subs it sold its Spectrum investment to. Those lease payments will be passed to bondholders. Oddly, a SPV has not been established to hold the asset.
Because it was so oversubscribed (30x) Sprint cut its interest rate from 4.5-5.0 to 3.375% (Fin Times)
The securitisation was the first of its kind (says the FT)