Nokia Sound Converter from certain versions of Nokia Suite should be able to convert NRT ringtones for use in MMS multimedia message Servic, i.e so you can send the audio via MMS. Seems probably old conversion that people needed years ago.
Convert Nokia ringtone to Multimedia Messaging Service message.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert nrt to mms on Windows
A set of applications used to manage older Nokia mobile phones
Convert from nrt file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.