Speakers: Monoprice for non-name-brand stuff.

iTunes: You don't need iTunes (open or otherwise) to play any NON-DRM iTunes-bought music that exists on a hard drive. The drive must be available to the network via a computer or NAS of course.

iPhone: You can't pull music from an iPhone to play on another device natively unless it's via AirPlay.

If you intend to play music that exists only on an iPhone (not from a networked computer/hard drive or NAS), the Sonos is redundant of course.