Natural disasters. After Katrina & Rita the digital towers went down. No one could call into the area codes for southern Louisiana and Mississippi. Now in some areas the land lines went down as well - knocked over by the storm surge or trees falling on the lines. While I was evacuated, I was "roaming" on my cell, so I could call out, but no one could call me. And then the towers would get clogged. Frankly I was happy no one could call me, gave me a modicum of control over my crazy life. But I couldn't reach anyone else (friends, colleagues) unless internet searches, gave me an alternate number to call. My land line was fully functional long before the cell towers were able to handle the load.