Well I can't say much about the iTrip, but if it's anything like their AutoPilot I wouldn't bother. I got one two days ago and it won't work at all in a crowded media market like LA because the transmitter is too weak. I'll be returning that one tomorrow for sure.
I'm having trouble finding any reviews of iphone FM transmitters that get decent scores. It seems to hard to get good clear reception on a station as you drive around.
Please let us know if anyone thinks differently & has a product they can recommend. I'd like to ditch my cassette solution because of the mess of wires.
I haven't seen any that claim to be 3G compatible. Just because they are made for the iPhone, doesn't mean they automatically work with 3G. My FM tuner/charger plays fine, but won't charge. I would check with any manufacturer before buying.
The autopilot works really well in terms of leaving Airplane mode on OFF and listening to music or internet Radio, while its charging, the Fm Transmitter is a little weak, but with a little research on http://www.radio-locator.com/cgi-bin/vacant you can find a nearly clear station.
It is a little expensive, retails for $100, but I found one on Amazon brand new for $70. And best of all its all on one cord.