WordNet sense 1 ((phonetics) an individual sound unit of speech without concern as to whether or not it is a phoneme of some language):

sound, speech sound

WordNet sense 2 (electronic equipment that converts sound into electrical signals that can be transmitted over distances and then converts received signals back into sounds):

telephone, telephone set

WordNet sense 3 (electro-acoustic transducer for converting electric signals into sounds; it is held over or inserted into the ear):

earphone, headphone, earpiece

WordNet sense 4 (get or try to get into communication (with someone) by telephone):

call, ring, call up