Katarina's Hurricane put forward a weakness in Voip network : since it is mainly relying on power, most of devices where out of order except a soft phone used by New Orlean's Mayor to contact outside was more an exception :

Read : BellSouth’s Smith: VoIP no miracle cure for Katrina by Carol Wilson from Telephonyonline.

On the other hand, the telephony service is being recovered quicker thanks to WiMAX through WISPs (Wireless Internet Service Providers) with VoWiFi :

Read : Long road to recovery begins after Gulf Coast hurricane by Carol Wilson from Telephonyonline.

As one can predict, satellite cell phones were the telecom device that kept the best service (read Hurricane Takes Down Telecom ) by By Caron Carlson and Carmen Nobel from eweek.com.

At least one of the telecom means was then still working in those extreme conditions. May be it is one more argument for network convergence ?