After reports that Apple had signed Warner Music Group and Universal Music Group to its much-rumoured Spotify rival iRadio, it is now said to have added Sony Music to the list of major labels it needs to give its streaming service a great start in a busy marketplace.

AllThingsD claims that a person familiar with the negotiations between the two companies has spilled the beans on the deal. It also says that the new music-streaming service will definitely be announced during Tim Cook's keynote address at the company's developers' conference, WWDC, on Monday 10 June - or in the early hours of Tuesday, if you're in the UK. It isn't expected to officially launch iRadio, however, just reveal it to the attendees.

It is believed that while Apple has signed Sony Music to iRadio, with artists like Beyonce and Rita Ora on its books, it is yet to get Sony/ATV on board, the firm's music publishing arm. That will still be a barrier to any possible full launch plans.

But with all the major labels being part of the action, that is surely now a matter of time.

Spotify, Pandora, Napster, Rdio, Deezer and the like will be concerned that a company of Apple's size, with its expertise and customer loyalty in music sales through iTunes, is about to muscle in on their turf too.