I didn't realise this, but...
...I can use BBC iPlayer (radio) via AirPlay on my iPhone 4.
I was Googling for updates on the progress with the BBC iPlayer app for iPhone. (There is one for iPads but not for iPhone yet.)
Anyway, nothing found, so I decided to just get iPlayer on my iPhone using Safari and play the latest 'Clare in the Community' episode with the iPhone plugged into the M-CR603 with USB.
Just as I was getting the lead from the drawer, I noticed the AirPlay symbol appear on my iPhone display, just as it would on iTunes
Being a bit 'thick' about all things AirPlay, I had assumed it was only for iTunes and would not work on BBC iPlayer (especially as it was accessed via Safari and not an Apple iPhone app.)
Once 'Clare' has finished, I am going to see if any old internet radio station, called up from Safari, works via AirPlay too. (Radio Paradise especially.)
I know I have internet radio on the Marantz anyway (and iPlayer via the Sony BDP-S370) but it's so much handier to do it all via the iPhone.
BBC iPlayer radio (on my iPhone) appears to be using QuickTime so I am assuming it is AAC. It certainly sounds ruddy good!
This is fun.