On the face of it using mobile phones for disaster communications does not seem a good idea. Most mobile phones are designed for city use, have very small antennas giving them a short range and rely on there being a high cell tower to relay signals. Walkie talkie CB radios are available for less than $100 which are designed to work on their own or with a low cost repeater for longer range communications. These can be set up quickly for use in a disaster area. Emergency workers can also be issued with more sophisticated "trunked radio" which has similar features to cell phones but are also designed to operate in more primitive conditions.
However, not all workers can be issued with a radio in a disaster zone and new communications procedures are needed to use them. Also low cost two way radios do not provide text messaging or computer interfaces. It would be much easier if workers could use their existing cell phone, with SMS as also access to the web.
It is a little misleading to describe the Serval project as making use of cell phones as it is the WiFi radio function of the smart phones being used, not the cell phone radio. The technique used is the same as used by OLPC computers which have a mesh network installed. In effect the service provides data transmission and then voice calls can be carried over that network. In a disaster it is likely that bandwidth will be limited and the system will mostly be sued for SMS and data transmission. The bandwidth needed for one voice call would service hundreds of SMS users..
What might make the system more practical would be use of external antennas on the smart phones to extend their range. This could be combined with a rugged case to protect the phone. While these would not look fashionable, there might be some kudos for volunteer emergency workers to have a bright yellow rubber covered phone with a whip antenna to show they are ready to help the community.
Also while the current project is concentrating on Andropid Phones, there is no reason why Apple iPhones, iPads, laptops netbook computers could not use the same system.