I use Katrina as my starting point for speculation and planning about things going horribly wrong in a natural disaster. Here's an article from way back when:
http://www.washingtonpost.com/wp-dyn/content/article/2005/11/07/AR2005110701334.html
When Katrina hit New Orleans, the 911 call center had to be abandoned because of the flood. They thought calls were routed to the fire department, but it was abandoned, too. Eventually calls went to Baton Rouge's 911 center without them being alerted to the fact - they had no clue where people were calling from and what any of the addresses meant. I consider this a total failure.

We live in the San Francisco Bay Area, so my assumption is that we'll have a major earthquake instead of a hurricane, but with global warming you never know. We have a landline at home, and we each have a cell phone on a different carrier in case one goes down, but the other survives. My assumption, though, is that all lines will either be out or so swamped we won't be able to get a dial tone.

Louise and I are ham radio operators, so we have plans on communications if landlines and cell towers are down. We have general licenses and two HF radios withbatteries and antennas, so we figure we can get hold of some hams out of the area of destruction.

We camp in Death Valley occasionally, and we rent a satellite phone, which has come in handy a couple of times (no emergencies). We can't afford to maintain an account, though, and I figure we won't be able to score a satphone after our major earthquake. :->

Any thoughts on communications if you can't get a dial tone? Something other than amateur radio? What am I missing?

Our goals are to let family know we're okay (they live out of state) and maybe get notice out of survivors' names -- health and welfare traffic. I don't think we'll be able to get any real help for emergencies from fire, police, or ambulance, but who can tell?