I installed a Z110BT in my 2006 GLI back in December, so I think I'm pretty qualified to answer your questions. I've upgraded my unit, so I basically have a Z120. Here goes:
- I have an iPhone 4, and it works pretty well. I've been really enjoying the PandoraLink feature lately, but it has some minor issues. The main one is that the phone will lose connection with the unit and will stop displaying the song info until the USB is unplugged and plugged back in. For some reason, I can't get the iPhone AVIC Feeds app to send destinations via the bluetooth, but I haven't looked into it really.
- In my install, I used the Connects2 CTSVW002 to get the steering wheel controls, ignition wire, and all the other signals that are on the CAN bus. I did a lot of research, and found that I preferred this over the PAC adapter. As far as I'm aware, neither option will make the phone button on the steering wheel work. With the Connects2, the mute button attenuates the volume of the Z110 (i.e. lowers the volume, as opposed to completely muting). I think this is a function of the Z110, not the adapter.
- Voice dialing is achieved by pressing the little button on the bottom left of the Z110. I REALLY wanted this to be activated via the steering wheel, but I just don't think it's possible. However, I've found that it's not too bad using the button on the unit.
- The Z110/120 uses it's own internal voice dialing, which is pretty good for me.
- The interface cable does charge the iPhone.
- The most difficult part of the install was the Sirius equipment. I wanted to use the OEM Sirius antenna in the shark-fin, so I ended up mounting the Sirius SCC1 in the trunk where the OEM Sirius unit was installed. I used a GM XM to Sirius adapter to connect one of the leads from the antenna to the SCC1 and then found an extension cord to allow me to run the cable between the SCC1 and the Pioneer CS-SB10 from the trunk to the dash. I mounted the GPS antenna in the dash on the metal beam that's running behind the upward vent. The USB/3.5mm ports were installed in the center console in the compartment underneath the armrest. I can take some pictures if you'd like.
Here are the parts I used in my install:
CAN/Harness Adapter:
http://www.incarexpress.co.uk/view_prod ... o=CTSVW002
http://www.incarexpress.co.uk/view_prod ... IONEERLEAD
Aerial Adapter (dual lead - make sure it's correct for 2008):
http://www.incarexpress.co.uk/view_prod ... o=CT27AA25
Fascia:
http://www.incarexpress.co.uk/view_prod ... =CT23VW01A
GM XM to Sirius antenna adapter (for Sirius):
http://www.tss-radio.com/sirius-single- ... -7025.html
Starbase SCFM1 8 pin Din Extension Cable (for Sirius):
http://www.tss-radio.com/starbase-scfm1 ... -4448.html
I hope that helps 
Thomas