Most of the large paging networks use a sat in their system, but the pager does not talk directly to it, nor does it directly receive from it. You transmit and receive via ground based equipment, that in turn is relayed up to the sat and then back down.

The reason that Skytel is so popular is that all of the other paging providers were on the same bird in 2000, when that bird died. Paging service went away for the large carriers (except Skytel, which was using a different bird). They had a backup bird, but a tech needed to go to each ground site and move the dish to see the new bird. So, it took a couple of days before service was restored.

Your text messages outbound may go through the cellular network, or a ground-based data network, before they get to the bird for transmittal back down to the paging network. The advantage to two-way pagers is that the network will continue to try to get the message through (usually) until it gets a confirmation from the receiving unit. One-way paging does not (and cannot).

Communications redundancy is no different than knowing multiple ways to start a fire, or carrying more than one blade. Consider these options:

2-way pagers (pager to pager transmissions)
Cell phone w/ text message capabilities
E-mail to pagers or cell phones
E-mail to free e-mail account (like Yahoo or G-mail)
Changing your voice mail greeting after an incident (lets people know that you are OK, and may let loved ones know where you are going. For example: "Hi, this is James, and yes, I did survive the earthquake, but the house did not. I am going to location number four.")
Ham Radio
Sat phone.
Out-of-area contact person to leave messages with.
Local place to leave messages.

Hope that this helps.