Ringtones Won't Ring

Thanks for taking the time to reply. I followed your advice and found
the ringer ID menu. It was already turned on, so I tried it on 'off',
then back again to 'on', but the ringtones I put on the phone won't
work as ringtones; they will play back when selected, but the phone
will revert to the 'default' ringtone if I assign these mp3 sounds to a
caller ID. Anyone got an idea? I see some messages about 'unlocking'
but I assume that if for the sim card and the service provider access.
Thanks again,
AL