Sony Music has signed on to Apple’s forthcoming iRadio service, according to a person familiar with negotiations between the two companies. The deal means that Apple now has agreements with all three major music labels. Apple had been pushing music executives to come aboard in advance of its annual developer conference next week, so you should expect to hear an official announcement Monday. It’s still possible that Apple may have hurdles to clear. As of earlier this week, the company had yet to sign up Sony/ATV, Sony’s music publishing arm. But the gaps between Sony/ATV and Apple were supposedly smaller than the ones Sony Music and Apple were looking at a few days ago. I’ll update on that deal if I learn more. Apple has previously signed on Warner Music Group and Universal Music Group, the two other major labels.