Fitted the Parrot CK3100 kit and its excellent. For the steering controls I used a Parrot Multican unit specifically for the 3100. Noticed on the spec that other than the CAN hi/low connections it had a K Bus connection as well. This did not appear to be advertised by Parrot even when I spoke to them.
Bit the bullet and bought one. Hooked it up and now the steering wheel telephone button works fine as does the volume control. Doesn't do everything the manual states and this is why they probably do no suggest it as a fitment.
But I can redial last number, end a call, start voice activation and control the volume. More than enough for £50 and an easy install.
So if you are content with some basic functions then go for the multican.
Please note R/T still has no function with this set up.