In the US most long haul disaster radio communications between state EOCs, FEMA, military and NGOs use digital modes.
A list of nets can be found here:
http://hflink.com/nets/
A description of automatic link establishment (ALE) can be found here:
http://en.wikipedia.org/wiki/Automatic_l...ablishment
A comparison of common amateur radio digital modes can be found here:
http://www.pactor.com/compare.shtml
The mode used by FEMA and the military is MT63, which is also used by amateurs who are enrolled in the Military Affiliate Radio Service (MARS)
http://www.navymars.org/central/reg4/al/MT63.htm
A tutorial for using MT63 is here:
http://www.navymars.org/national/trainin...ning_3.pdf