Yes, it worked on my P4000, but I sent it back and got a refund. Sound was muddy and staticy and the charger itself was only a 250mA charger, not enough to charge the phone but enough to power the transmitter. Transmitter will NOT work without plugging the charger in. So while you listen to it thru your FM radio, your phone battery is draining and you can't charge the phone unless you take the transmitter out.
I went with a cassette adapter for my car. SO much better with an adapter that changes the headphone jack into a 3.5mm jack for the cassette adapter. If you have an aux input in your car stereo, you can use that instead. Still a LOT better than going thru your FM radio.
If you use the 1 into 2 adapter that comes with the phone, you can charge your phone at the same time with one jack, and the other jack with an adapter can be used to run the sound out.
The adapter I am talking about can be found at the link below. This also comes with a built-in microphone so you can use it hands free while driving.
http://cgi.ebay.ca/3-5mm-Headset-Hea...QQcmdZViewItem