When cellular service is not available the phone can switch to satellite operation. This is the way the coverage works in China and Japan. When using the PSTN the phone has to be compatible with the standards supported by the PSTN or local mobile service with whom GlobalStar has service agreements. The phones are multi-mode and work with terrestrial AMPS, CDMA, or GSM networks, as well as the Globalstar satellite network. This overcomes the problems of incompatible standards in use around the world, since one can always fall back to using the satellite mode.
Phones equipped with a satellite receiver tend to be relatively large and bulky.
Also there can be problems with satellite reception when indoors. Given the rapid changes in technology and service offerings, it is hard to make a long term recommendation. We also feel we need to understand the issues more and thus need to experiment and learn more about the services. For travelers to Japan, renting a cell phone at the airport seems to be the best option. It would be useful for somebody to try this out to determine whether it is easy to do, what it costs, and how it works.