it was a category in their ring tones contest. they have three boot up sounds, which has absolutely no real use.

fun fact, it was originally included in older phones as a marketing gimmick, a way to generate more revenue. someone at nokia or siemens had the idea to sell it to operators the same way as an Ad spot is sold. telco operators paid manufacturers to have their jingle there instead. and in markets without buyers, they put in the manufacturer jingle as a placeholder.