OK so a quick update, I thought I'd test with all USB (Class ID) blocked in place of the smartphone in the DC element of this policy and no luck.
So what I have deployed is as follows Device control blocking the Smartphone class ID, application control making removable storage read only and also blocking iTunes.
With this policy in place there is no visibility of the iPhone 4S or 5 and both phones continue to charge.
All this from installing a 3rd party utility on the client which increases the voltage to the USB port. Without this utility and with the same policy applied the phones do not charge.
It does what I need it to do, so I thought I'd share...and before you guys ask I have made the Product Managment Team aware of this.