No signal and Network listed as Not Available

My wife has an iPhone 5 on the Sprint network. Last night, she couldn't get a cellular signal (it simply said "Searching..." in the top left corner). I tried the usual tricks, toggling airport mode, resetting network settings, soft reset, hard reset, nothing had any impact.

I then also noticed that when you look at the Settings->General->About screen that the Network is listed as Not Available, rather than Sprint.

Any thoughts? Thanks.