Nokia N9 has the Fm transmitter, but there is no antenna or software for it. May be that someone comes up with a solution someday.

N9 is a successor to the N900, so I would recommend you to buy N9. It's "Open source system" like n900. In time you will get all n900 best apps in n9, and more.

N9 has no keyboard, infrared and (Fm-transmitter software). Thats all things that are missing in n9, what were in n900. However, N9 has more effective hardware.

And let's hope the N9 Fm-transmitter would work one day