In my opinion there is no good solution for the iphone...
1. Aux cable / Cigar lighter charging cable and a windscreen mount (problem is wires everywhere, windscreen mount attracts theives thinking you have tom tom)
2. Change the snap in between the seats (cant operate while driving change tracks etc)
3. Intravee / Dice (expensive and limited when you already have a great screen on iphone but good part is it allows control of iphone through nav in a limited way)
4. Bluetooth A2DP Reciever Over the air plugged into aux (great but iphone battery dies if not being charged you also need a mount then you are back to 1 plugging charger in with wires)
my solution:
5. Custom iphone holder in cup hole connected to AUX and charging from wiring behind dash taken from cigar lighter. Can also be used as Navigation with the 19.99 app co pilot which my girlfriend uses and its faultless.
All i did was buy one of these http://cgi.ebay.co.uk/DESKTOP-CHARGER-DOCK-DOCKING-STATION-IPHONE-4-4G-/280584306326?pt=UK_MobilePhones_MobilePhoneAccessories_MobilePhoneChargers&hash=item415420be96#ht_1183wt_907
and then one of these http://cgi.ebay.co.uk/Cigar-Lighter-Car-Charger-USB-Convertor-Adapter-New-/330567279948?pt=UK_MP3_Player_Accessories&hash=item4cf758654c#ht_1773wt_907 soldered to it directly and taped up and hid it below the ashtray taking the feed from the back of the cigar lighter, then just ran the AUX cable to it directly behind the dash.
Cut away a hole in the existing blanking plate for the cup holder and then using high powered glue, glue the top of the dock to the bottom of the vent. This is all reversible too if you go buy another plastic blanking plate from BMW as the glu would not be visible.
https://picasaweb.google.com/103012469849143820414/TheZ4ICupHolder?authkey=Gv1sRgCKjGi5XW3dmwbw
btw pictures are wonkey, from drivers seat the phone sits straight and tilted inwards for perfect view. Of course you have to turn the vent off otherwise you get the temp warning on the iphone come on lol
finally music everytime i get in the car and no messing around anymore!

1. Aux cable / Cigar lighter charging cable and a windscreen mount (problem is wires everywhere, windscreen mount attracts theives thinking you have tom tom)
2. Change the snap in between the seats (cant operate while driving change tracks etc)
3. Intravee / Dice (expensive and limited when you already have a great screen on iphone but good part is it allows control of iphone through nav in a limited way)
4. Bluetooth A2DP Reciever Over the air plugged into aux (great but iphone battery dies if not being charged you also need a mount then you are back to 1 plugging charger in with wires)
my solution:
5. Custom iphone holder in cup hole connected to AUX and charging from wiring behind dash taken from cigar lighter. Can also be used as Navigation with the 19.99 app co pilot which my girlfriend uses and its faultless.
All i did was buy one of these http://cgi.ebay.co.uk/DESKTOP-CHARGER-DOCK-DOCKING-STATION-IPHONE-4-4G-/280584306326?pt=UK_MobilePhones_MobilePhoneAccessories_MobilePhoneChargers&hash=item415420be96#ht_1183wt_907
and then one of these http://cgi.ebay.co.uk/Cigar-Lighter-Car-Charger-USB-Convertor-Adapter-New-/330567279948?pt=UK_MP3_Player_Accessories&hash=item4cf758654c#ht_1773wt_907 soldered to it directly and taped up and hid it below the ashtray taking the feed from the back of the cigar lighter, then just ran the AUX cable to it directly behind the dash.
Cut away a hole in the existing blanking plate for the cup holder and then using high powered glue, glue the top of the dock to the bottom of the vent. This is all reversible too if you go buy another plastic blanking plate from BMW as the glu would not be visible.
https://picasaweb.google.com/103012469849143820414/TheZ4ICupHolder?authkey=Gv1sRgCKjGi5XW3dmwbw
btw pictures are wonkey, from drivers seat the phone sits straight and tilted inwards for perfect view. Of course you have to turn the vent off otherwise you get the temp warning on the iphone come on lol
finally music everytime i get in the car and no messing around anymore!

but hey its an idea!