I have checked this also in a real phone. Most Nokias with radio built in use a Philips chip (the TEA5767) which contain an FM receiver with analog stereo decoder. They have used this chip before in series 40 phones such as the 3200 and 3300. The only thing the 6260 has is a stereo headphones amplifier and an analog mixer digitally controled by the Symbian Os that feeds to the audio amplifier either the mono DAC used for voice coding and Symbian applications or the FM radio. They have cheated all of us that bought the phone assuming that it plays MP3 files in stereo. They carefully omit the detail wether it plays audio files in stereo or mono, only claim that the RADIO is stereo.
Cheated?? really? I beg to differ. If they didnt state implicitly that it is MP3 Stereo, then you cant claim they made you think it is. From a legal standpoint, there isnt much of a case.
Also, really, people should do research on these things. Befor you buy, find out about it in depth. Dont jump to conclusions without any info to back it up.
It most definitely does not play MP3's in stereo! You can easily verify it by making a stereo MP3 file with clearly different content for the left & right channels. Use, e.g., Audacity (http://sourceforge.net/projects/audacity/) to make such file and hear for yourself.