WordNet sense 1 (sing (each note a scale or in a melody) with the same vowel):

vocalise

WordNet sense 2 (pronounce as a vowel):

vowelise, vowelize

WordNet sense 3 (express or state clearly):

articulate, enunciate, articulate

WordNet sense 4 (utter with vibrating vocal chords):

sound, voice

WordNet sense 5 (utter speech sounds):

phonate