I've relied on these forums a lot in the past and haven't really given much back. So here's a little bit on how I got an auxiliary, USB and Bluetooth phone connection and audio into my car. I would like to apologise for not having any pictures as I did the install a while back and only decided to write a post recently, mainly due to the excellent product.
So about 3 months ago as my A3 is an 04 plate I was getting quite annoyed with the stupid tape adaptor I was using to get audio to play from my phone through the car speakers. So I started having a look around to see what was available to get a better/cleaner looking connection to the car through either auxiliary or Bluetooth. I looked at many options starting with the Parrot Bluetooth Audi systems, and also the Denison Ice>Link, along with some other boxes that could be plugged into the back of the head unit. I even considered hacking together an auxiliary connector that I would then stick to a blank button plate on my centre console, however gladly I decided against that. Most of the pre-made connection systems were quite expensive and it seemed a large number of people had had issues with various elements. The Parrot in particular if not installed correctly would only use the front speakers and it's own amp to play your music which did not seem worth the money for me at all. Of course there was ways around this but the hassle seemed too much.
I finally found a little black box from Grom Audio, I researched it heavily and it seemed since the original MK1 boxes people had been having relatively good experiences. They are now on MK3 and I cannot recommend the box enough! The box also comes with a USB and auxiliary cable that can play files from a flash drive. I wanted a USB port to charge my iPhone as having a goofy cigarette car charger was also annoying me. I bought this box for my Audi A3 2.0TDI with Symphony 2 head unit (built in CD changer):
Audi / Seat / Skoda / VW - Aux-in adapter kit [GROM-AUX3-VAG] : Carputer-Shop | iPod Car Kits | Aux Adapters
I then added on the Bluetooth extension dongle and the AUDS loom extender (means you don't have to cut your existing loom to use the empty CD changer slot). The reason I chose to buy the AUX3 system and then add on the Bluetooth dongle rather than buy it built in was because it allowed the microphone to travel slightly further and also I could place the Bluetooth module in a slightly better place away from the back of the head unit which I feared could result in range/interference issues. This all came to £110 (£5 P+P).
Installation is very simple, however if like me you want a clean install and the microphone hidden away it will be slightly more difficult, but only slightly. The box itself plugs into a mini ISO port on the extension loom and the previous ISO connector from the car plugs into another part of the extension loom. The extension loom then connects to the head unit. Now comes the placing of the wires, I chose to pass the auxiliary and USB cables down into the tray I have underneath the front centre console section, I'm lucky in that I have the Non-smoking pack factory fitted, so it may not be a suitable place to pass wires here for those with an ashtray. This then meant I could push back wires when I didn't need them but they were still easily accessible.
The next and hardest part was the wiring of the microphone... Me being me I like everything to look clean. So I chose to mount the microphone behind a grill in the light cluster in the headliner. It first required running the microphone wire underneath the steering wheel up the a-pillar across the headliner and out to where the light cluster attaches. Getting the a-pillar cover off was scary but fine, just pull hard and slowly and the clips will come out, then you need to slide it up to release it. I also made sure to cable tie the wire behind the a-pillar airbag as it's pretty obvious you don't want anything obstructing a freaking airbag! I used a length of thick but bendy metal garden twine to make sure I could get the wire through the way I wanted, then I taped the mic wire onto the end of the garden twine and pulled it through. Bit fiddly but not difficult at all, your hands may be a bit cut up after running it under the steering wheel though!
Mounting the microphone in the light cluster I had to cut a little of the plastic from the fitting to get the microphone to fit, but it was pretty straightforward for anyone willing to use a Stanley blade and a drill, don't worry about drilling too much as the piece the microphone is mounted in is hidden with grey coverings when everything is fitted back. It's all a matter of trying to position the mic how you want it and then removing the plastic obstructing it. There is also a sticky pad supplied so if the mic is a little use you can always stick it down with that also.
After everything is fitted it's a very nice system to use. The Grom audio is selected by hitting the CD button on the head unit once if already playing CD's or twice if on radio. Now you can play any input you like. Bluetooth pairing is also straightforward with the box available for pairing for 3 minutes after the car is started and requiring no passcode. My iPhone 5 has the connected automatically every time I've gotten into the car. Music audio quality is excellent, easily CD quality and I'm a sound nut so I would state any issues I'd had if there were any. I have also tested the Bluetooth call quality with multiple people and all have said that it comes through loud and clear, with the only problem being told my numerous people I tend to shout a little because I think the microphone will struggle ha! You can actually answer calls by pressing the next track button when one comes in, and end a call by pressing back track.
So yeah like I said, just wanted to share my experience and hopefully quell any worries other Audi owners have who are thinking of buying one of these. Really really good product! Delivery is quick and customer service good from carputer-shop as they are the UK distributors of Grom Audio products. There is also a basic installation guide supplied with the box.
Sorry it's a bit long, but for anyone interested in this box it's hopefully worth the read!