When all other forms of communication have been disrupted or are not available satellite phones give you reliable voice and data communication.
This is possible because satellite networks do not depend on ground based communication. If you and/or your communication group use the same satellite service provider i.e. Globalstar you should not have any problems communicating. Calls are handled by the Globalstar ground stations and do not use the public phone network. If you do need to communicate with another Globalstar phone outside the coverage area of the ground station serving that phone, then the call can be switched through dedicated T1 lines to another Gateway where the call is transmitted to the receiving Globalstar satellite phone.
In most cases areas of communication disruption is in a localized area. A good example would be New Orleans where hurricane Katrina made land fall and devastated the area. In this case if you were using a Globalstar phone all calls from Globalstar phones to Globalstar phones were completely handled by the Clifton, TX ground station. The call would go to one of the satellites in the Globalstar constellation then basically reflected down to the ground station where it would then be sent back up to one of the Globalstar satellites then down to the Globalstar phone receiving the call never using the public phone network. The Globalstar network is made up of 48 low earth orbiting satellites.
The Iridium network call process is different than the Globalstar network. Unlike Globalstar where all the switches and most of the call handling is made from the ground station... most of the switching and call handling is made by the Iridium satellites themselves. Iridium to Iridium calls are handled in this way, calls will go up to the Iridium satellite then may travel from Iridium satellite to Iridium satellite till it reaches the receiving Iridium satellite phone never using the Iridium ground station or the public phone network. With this type of call the Iridium constellation completely handles the call. The Iridium network is made up of 66 low earth orbiting satellites that follow a polar orbit.
Calls made between competing satellite phone companies can be very difficult because the public phone network must be used which could be disrupted. An example is if a Globalstar phone calls an Iridium phone the call goes up to a Globalstar satellite and it is sent down to a Globalstar ground station. The ground station then must switch the call to the public phone network where it is carried to the Iridium ground station in Arizona. The call is then sent up from the Iridium ground station to one of the Iridium satellites where it is switched to the receiving Iridium satellite phone. If the public phone network is disrupted between the two competing gateways then it may not go through. This is why it is best for your communication group to use the same satellite phone provider.