Microsoft has added 400,000 subscribers to its MSN Internet service during the last six months, boosting its total subscribers to 6.9 million. Number-three ISP EarthLink, which has a partnership with Apple, has about 5 million subscribers. Unlike MSN, however, EarthLink has added relatively few new dial-up subscribers during the most recent quarters. Microsoft attributed the significant boost in membership to its campaign to lure customers away from rival ISPs, particularly America Online.