Complex sentence: Participation in SKYWARN does not require an amateur radio license; more than half of all SKYWARN spotters are not licensed for amateur radio and instead make their reports via telephone or the Internet when those are still functioning.
Split into simpler sentences: Participation in SKYWARN ™ does not require an amateur radio license; more than half of all SKYWARN ™ spotters are not licensed for amateur radio. Those without a radio capability make their reports via telephone or the Internet when those are still functioning.