Similar to a blowjob, in which one uses the mouth to stimulate the sexual organ of his/her partner. However, rather than there be physical contact between participants, the person performing the yelljob uses the mouth to produce specific frequencies, which will then cause the sexual organ in question to vibrate, causing great pleasure. One can use various frequencies, depending on the situation. Often, simple melodies are effective or various tones. The yelljob is often performed by abstinent couples, who want a pleasurable and memorable experience, but do not want any physical contact of any kind.
Dude, Portland's own Hailey Niswanger gave me the greatest yelljob last night with her own rendition of Skylark. My dick is still ringing!