It's fine to use an iPod charger. In fact, when I was buying an "iPhone car charger", the Apple Store clerk asked if I already had an iPod charger. I told her I did, and she said that I could use that. That saved me a few bucks.
All my old iPod products - chargers, speakers etc., work with my iPhone. It pops up a message to say that the device is not approved and asks if you want to switch to airline mode, but that's it. Say yes or no, as you prefer, and it all works fine.
The iPod input that I installed for my car a couple years ago works great! It charges the phone or iPod and allows me to listen to the iPod/control it through my steering wheel and car's display.
Ok...I was just wanted to make sure cuz I didn't want to mess anything up. Because the ipod hook ups have the buttons you have push in to retract the metal hooks and the iPhone one doesn't.
All my ipod car charger and radio dock will charge my phone too just fine. My only problem is my dock is not compatible and requires the phone to be in airplane mode if I want to listen to music . Looks like I gotta wait for a newer, compatible model...