ring-back tone
n.— «In Asia, where sales of music to mobile phones outpace CD sales in some places, labels may offer more than 400 different items in connection with a specific album, including ring-back tones—snippets of music that play to callers while they wait for their call to go through—or “color call” tones, background songs that play while someone talks on the phone.» —“Squeezing Money From the Music” by Jeff Leeds New York Times Dec. 11, 2006. (source: Double-Tongued Dictionary)