The question of emergency BOB communications is a tough one. If you wish to broadcast an SOS message, then someone has to be listening to firstly pick up the message then to pass that message on the appropriate authorities to initiate a rescue. This might be difficult if the emergency is wide spread. But if the emergency is very widespread then it may be best to look into the resiliency of what is out there already. GMRS/FRS has limited range for broadcast and limited power RF capability for what is a UHF frequency line of sight system as hand held sets are typically rated 5W for GMRS and 0.5W for FRS. If the communications system is to kept within a vehicle then portable power requirements are not a problem, but as soon as the vehicle is left behind then power requirements for transmission and reception of a radio signal now become pretty crucial.

I would look to use the current infrastructure that is already in place i.e. the cellular phone network and the fixed line POTS. The probability of making contact with a cell phone tower over a GMRS/FRS user will probably be much higher. Once you have established the hand shake with the tower you will then have access to contact billions of users worldwide. If you contact another GMRS/FRS user the problem of passing the message you want to send to the end user you want to send the message to will most likely have failed as well unless the other GMRS/FRS user has direct access to the already currently installed infrastructure of cellular and POTS telephone systems. You also will then have access to SMS messaging and potentially email and Internet services as well.

The same issues apply to Citizens Band Radio on the 27MHz but radio propagation on the 27Mhz CB system has the potential to propagate further, but with the issue of less monitoring of the radio signal broadcast.

Rather than spending cash on either CB or GMRS/FRS for an portable BOB emergency comms system then I would spend the cash on a directional gain antenna for a cellular phone and a means of powering the cell phone from a renewable source i.e. a solar panel/battery setup such as a Sunlinq solar panel and an external battery store such as an iSun AA BattPak

http://www.dealextreme.com/p/2-4ghz-800-...-n-female-29507

http://cellantenna.co.uk/index.php?id=yagi