Hmmm, it seems it is not quite how I thought. 3230 and 6260 don't play MP3 in real stereo after all, only mono sound is divided into two earpiece, even if the FM radio is stereo. Whereas at least Nokia 6630 and 6620 have a real MP3 Stereo. Sorry for the misinformation.
It's a very pitty. I want to buy 3230 or 6260 but if they can't play real stereo a i won't buy them. And i haven't 500 Euro to buy 6630. (6620 is not in Czech republic). But why they can¨t play real stereo mp3? There's a hardware player or software player??? If it's software player, there is symbian OS, so i can install another aplication, which can play real stereo mp3. And can it plays another formats in real stereo? Perhaps *.aac,ra,rm,ram,ogg,wma.......... I want to know it. Because nokia 6260 is very nice (maybe the camera would be 1 megapixel).
It is a matter of hardware. The FM radio chip & related DAC (Digital/Analog Converter) has stereo output capability, but for the software based MP3 player (or any other software) it is not possible (and cannot be changed without redesigned hardware).