The following will apply to OBi1022, OBi1032 and OBi1062:
-Go to the phone web page: at phone screen, arrow to Settings for Network IP Address. Input IP Address in your browser address bar and hit Enter on keyboard. (Best to use Chrome).
Go to "Voice Services / Auto Attendant".
Select one of the user prompts, for example 3, and click on User3Description.
This will bring up a page to allow one to upload an audio file.
MOST IMPORTANTYLY, supported formats:
.WAV or .AU, 16-bit linear (uncompressed) or ALaw/ULaw encoded, mono or stereo, at 8/11.025/16/22.05/32/44.1/48 kHz sample rate.
-Go to "IP Phone / Phone Settings".
Set "MOHServiceNumber" to an($$%USER3%) in the above example where you loaded the file to user prompt 3.
NOTE: to convert to supported formats, for example, use Audacity software at link: http://www.audacityteam.org/download/windows/
Please let me know if this will work by your response/comments.