A handheld satellite phone with a charged battery will work in all areas where a power disruption has occurred. With a handheld satellite phone without an outside antenna you must use the phone outside away from large structures and trees. Having an 80% view of the sky will give you the best results when using a satellite phone. You must have line-of-site to a satellite to be able to complete a call.
If during a power interruption cellular and landline service is disrupted you will not be able to call any cellular or landline that has been effected. Your satellite phone could be fully functional, but it will not be able to complete a call to any other communication service that has been disrupted.
When using a fixed site satellite phone you will need a battery back up to use the phone during a power disruption. Fixed site satellite phones are normally used when satellite communications is needed indoors. An outside antenna is required with a fixed site unit to obtain the line-of-site needed to communicate.
In an organization where emergency communication is necessary it is important for your communication group to use the same satellite phone service. Using different satellite phone services within the same communication group can cause confusion because different satellite phones have different call patterns. The Globalstar satellite phone when used in the US or Caribbean uses standard North American dialing patterns, an Iridium satellite phone does not. The cost of calling from a Globalstar phone to an Iridium phone can be costly because there is a separate per minute rate when calling an Iridium phone which is not included in your standard minutes.