A wireless communication system including flexible wireless handsets with modular electronic components selected for operation within multiple systems. The units may be configured for removable connection to a variety of cartridges to provide a versatile communication device. A cartridge may be selected for the replacement of one or more existing cartridges within the handset to provide varying degrees of flexibility including the selection of a different featureset for the handset and compatible operation within different wireless systems. Methods are further provided for upgrading and reconfiguring cellular telephones and wireless communication devices for operation within different systems. A flexible wireless telephone with an original removable cartridge may include later-substituted cartridges to improve or change the featureset of the telephone, and may also enable a user to replace the internal electronics of a handset with different internal electronics for use within a different wireless system. A consumer may be thus provided with extended use the same flexible wireless telephone handset yet still migrate to a new wireless system by installing cartridges with desired featuresets within the selected wireless telephone system(s).