There is already a working version of the fmradio for Android 1.5 versions of the phone, but the same apps don't work for 2.1, apparently the kernel must support it and the leaked one doesn't. Is the flipout cupcake, or eclair? I am waiting the 150secs until the download starts before I can found out ;-)
edit:
interesting! ro.build.description=umts_ruth-user 2.1-update1 RuthGC_0.18.4 100714 release-keys
ro.product.cpu.abi=armeabi-v7a
ro.product.cpu.abi2=armeabi
I will give it a try and let you know.
It seems xt502 using Qualcom chip.
I will check with others on the chip and FMRadio.
If it is Qualcom and FMRadio inside, I will try to get the firmware from somewhere.