As an interesting follow up to my comments on the reliability of SMS messages, some relatives of mine have been affected by the terrible fires in Canberra. In many instances they have not been able to make mobile or fixed line calls, due to networks being overloaded and damaged. However, they have been consistently able to get SMS messages in and out. Because SMS messaging only uses a tiny amount of bandwidth, and because it doesn't have to be in real time, SMS capabilities survive when a network is too overloaded or damaged to handle voice calls. (A workable SMS service is requires many fewer base stations than a workable voice service). Using SMS rather than voice calls is also going to preserve battery life in instances where people who are stranded have no access to power.

As an interesting observation, this might be an interesting way for telcos to promote the use of SMS in countries where its use isn't that widespread (ie the US). Promote it as something that people should learn how to do for the sake of safety. Hopefully, having then learned how to do it for the sake of safety, people will start using it for other reasons as well.

Of course, learning how to use it clearly is a good idea from the point of safety, so in this case everyone wins.