Most mobile telephone networks operate close to capacity during normal times and large spikes in call volumes caused by widespread emergencies often overload the system just when it is needed the most. Examples reported in the media where this have occurred include the September 11 attacks, the Hawaiian earthquake, the 2003 Northeast blackouts, Hurricane Katrina, and the 2007 Minnesota bridge collapse.
Also, terrestrial cell antennas and networks can be damaged by natural disasters. Satellite telephony can avoid this problem and be critical in natural disaster communications. Satellite phone networks themselves are prone to congestion as satellites and spot beams cover a very large area with relatively few voice channels.