On my old phone the ring tone was one of my friends going "Ring Ring", and this is not a ring tone I could possibly download from the ring tone store, also the phone only allows DRM protected mp3 files to be used as ring tones.
After a little bit of searching I found a solution using a bug in the phone software.
- Start the MP3 player (9. Tools -> 1. MP3 Player).
- Start playing the default song that came with the phone (1. All songs -> Beautiful Sky).
- While the song is playing, set the desired MP3 as the ring tone or message tone. (Options -> 3. Search -> MP3 File -> Options -> 3. Set As -> 1. Ringtone -> 1. Yes)
So now I can have my ring tone back.