I've had several reports that cell phone users who can't make *or* receive calls are successfully sending *and* receiving SMS. It could be
that the problem is one of not enough cell channels and working phone circuits for all the phone calls people want to make, but that the SMS channel is not overloaded and thus SMS traffic can zip on thru (when the
cell has power and can reach a working cell tower).
This was my personal experience during the July 7th terrorist attacks in London. I couldn't make or receive voice calls but SMS did get through both incoming and outgoing. However the delivery of SMS messages was sometimes delayed by as much as an hour. SMS takes far less network bandwidth than voice calls. Originally it was implemented as part of the control network of GSM (rather like SS7) but I believe that most carriers now simply use IP networks to carry their SMS traffic. By now it has become clear that the response to the New Orleans disaster has been completely screwed up because of lack of reliable communications in and out of the city. There are tons of food, water, medical supplies and personnel hung up on edge of the city because no-one seems to know what is needed, where it is needed, how to get it there, etc. --Michael Dillon