UNITED NATIONS (Reuters) - Geri Halliwell, formerly known as Ginger Spice, will become a goodwill ambassador for the U.N. Population Fund in Britain, a U.N. spokesman said Monday. Halliwell in May quit the Spice Girls, Britain's biggest pop phenomenon since the Beatles, because of differences with her fellow singers. She will appear at a news conference at the United Nations Tuesday and is to campaign for UNFPA with European Organizations on reproductive rights, U.N. spokesman Yasuhiro Ueki said. Considered the former leader of the Spice Girls, who have sold 30 million albums, Halliwell was noted for the biggest voice, the skimpiest outfits and most extrovert personality of the group. ###