I just looked at the external antenna connector on the back of the CDMA Treo 600 and also the Treo 300 by prying off the rubber plugs. They are different! The CDMA 600 has a larger and more robust connector than the 300. I hope the car kit for the 600 includes an external antenna and also hope someone with make an adapter cable for it.

I know for a fact that the GSM 270 does not have an external antenna connector. Can someone out there with a GSM 600 look and report back whether it has an external antenna connector? It's behind the rubber plug that is on the back and below the antenna.