depending on what sort of fone you have you can download tunes from www.nokia.co.uk this gives you the option of choosing the model of fone you have to download then your friend will have to ethier use bluetooth or send via message
I connect to my PC via a lead or bluetooth and send them that way, I usually send a full track as my ringtone, or you can get ringtones from P2P sites like Limewire, Frostwire or Bitlord