Sony signed its agreement late yesterday, and Apple plans to announce the service, unofficially dubbed iRadio, at a conference on June 10, said the people, who requested anonymity because the talks are private. Vivendi SA’s Universal Music and Len Blavatnik’s Warner Music Group have already signed agreements with Apple, people with knowledge of the situation said this month.

With the record companies on board, Apple plans to announce an advertising-supported service that will compete with Pandora Media Inc. for listeners. IRadio will allow users to build custom stations based on an artist or genre that draws on music from the company’s iTunes library.

Apple, based in Cupertino, California, fell 0.2 percent to $437.53 at 12:31 p.m. in New York, after sliding 18 percent this year as of Thursday. Pandora, based in Oakland, California, added 2 percent to $14.60 and had risen 56 percent this year.

Apple’s agreement with Sony Music was reported earlier today by AllThingsD. Sony/ATV Music Publishing, a joint venture of Sony and the estate of Michael Jackson, hadn’t reached an agreement with Apple as of earlier this week, the website said.