The handy thing about my old Escort was you could plug your phone charger in the ciggy lighter, send the end to the glovebox, shut it, lock the car & your phone will charge away happily.
The nuisance with the Astra is to do this - the key needs to be in the ignition, which presents an obvious problem. If possible, i'd like to have in a permanent charger, but i wouldn't know how you'd do it.
The rear of my HU is thus:
But the blue ended lead on the left connects into an iPod extension cable, which doesn't appear to be compatible with the iPhone 3GS. Even if it was, the problem of charging the phone whilst you're not in the car is still there (& the fact that i wouldn't be able to listen to my iPod).
We also all know what the iPhone charging cable looks like:
Ideally, i would like it to run into the lower DIN slot. I suppose it's possible, i just don't know how you'd do it.