My buddy has one of those for his iPod and the first morning i had the phone i tried to plug it in and the iPhone informed me that this type of hardware is not supported by the phone. I was kinda disappointed because i could use it with everyone else's iPod transmitters but its a no go.
I just bought a roadtrip specifically for my iPhone about three days ago. So far it has been working just fine. However, something interesting has occurred. I work at Best Buy and sold another iPhone user a roadtrip. We couldn't FET his to work. Everything about our two phones was the same, except for one thing: the OS version. He hadn't tipdsted his phone with the new patch yet. This is the only thing I could think of that was wrong. Hopefully an update will make it work properly.
One question, what is the Sound Check option in the iPod settings? With it on it makes the FM transmitter volume super low. Naturally I have it off so as not to have this problem, just wondering what its real function is.