I seem to recall that it was the cell phones that were functioning and the landlines that weren't in the katrina mess.
Cell phones were spotty at best after katrina. The phone companies brought in COWS as soon as they could. COWS — Cell On Wheels. Portable cell towers.
The land lines in most of New Orleans proper failed due to flooding and wind damage. The Mississippi coast that took the brunt of the storm surge had much the same problem. However, the cellular towers were down over a much wider area. The cellular companies couldn't restore the network fast enough; they didn't have enough portable equipment to handle such a widespread outage. For weeks, the cellular service in the 504 area code was down to text only. And I mean *text* only, no photo attachments were getting through.
In areas surrounding New Orleans, cellular service was out but land lines were okay. I think it's foolish to discontinue land line service, even as just a "test" or pilot program.