The MP3 option from factory is a typo in the UK alfa page. There is no MP3 option for the 147 from factory. There is however cd-changers and other options for mp3 but you have toinstall them yourself. Do a search of the forum on mp3 and you find that this topic has been discused. The fiat stilo has a connect system that has mp3 but the guts of the system is completly different, even made in a diferent factory, so do not get confused. IF you want mp3 the best todo is order the 147 with preinstalled cdchanger cable, I think is standard anyway, and install a SONY cd-changer that has mp3.
Again do a search and you will find all the info you need in this forum.