I've enjoyed having an FM radio built-in to previous phones, but obviously my Treo 650 doesn't have one.

Instead, I think it would be great if an FM receiver option could be added to "2-in-1" headset extensions (Seidio, Insten, etc.), as Sony Ericsson have done with their HPR-20 and the HPM-80 which ships with the W900i.

If it needed power from the main Treo connector, rather than from the 2.5mm socket, obviously it should be of the MMT design

The SDIO radio adapters are all very well and good, but because your headphones plug directly into the SD card, you can't easily cut in and out of phone calls as you can with the 2-in-1 headsets.