samsung sgh-p400 data cable transfer

Hi, my son has a Samsung SGH-P400 - I'm trying to download a ring tone from
my computer from 'another mobile' it appears to have a serial data cable
but I don't know how-to transfer this data can somebody can help.

Just to make this clear I've downloaded a ring tone from a 'mobile' to my
'computer' - I now want to transfer this ring tone to my sons mobile

Fluke