There has been quite a bit of mystery surrounding the FM Radio on the N900, but the good news is that it does have one. The bad news is that it is not so easy to enable. If you recall even the N800 shipped with an FM Radio onboard, but without software to utilize it, the FM radio application was a separate install.
Similarly on the N900, the hardware support exists but the software is missing. According to this post on Pycage, the hardware is disabled for power saving reasons and to load the FM Radio driver Bluetooth needs to be powered up along with the I2C communication bus.
Martin Grimme goes on to explain:
“After the driver has been loaded by the FMRX-Enabler, the FM radio provides two interfaces for controlling. A classic Video4Linux2 interface featuring only the basic stuff such as setting the frequency and muting/unmuting it, and a sysfs interface where you can read and write into file-like objects to control the radio.
Another tricky part is getting to hear sound from the radio. Unlike the N800, the FM radio doesn’t output to the speakers directly. You have to capture the sound from the PGA line and play it back”.
You can jump across to read all the other details. Martin meanwhile has uploaded the FMRadio application for testing which you can find here. Do keep in mind that, due to the nature of the processes involved to make it work, your battery life may see a significant impact.