Apple Inc. (Nasdaq: AAPL ) plans to unveil its new iCloud service at its Worldwide Developers Conference (WWDC) Monday - and Chief Executive Officer Steve Jobs will make an appearance to headline the event. In an extremely unusual pre-announcement Tuesday, Apple said Jobs will be on hand to introduce the company's new cloud services offering, which will allow users to access music and other media over the Internet. Jobs has been absent most of the year since taking medical leave in January for the second time in two years, except for an appearance in March to introduce the iPad 2 and a few recent interviews. Jobs usually keeps information on new products tightly under wraps until they are officially unveiled, but Apple posted a conference preview on its Web site that mentioned the iCloud offering .