This forum is hosted by NCH for user-to-user support, but is not the best way to inquire about the company's products. WAV is a general audio format and WAV files may be attached to messages, but mail client software generally won't know if the file is speech or music. To convert speech audio to text requires voice recognition software, which will make errors if not trained to a particular voice. Music files for songs registered in internet music databases may have associated lyric files that can be retrieved and displayed via a plugin to a media player.
I haven't seen any product specifically designed to convert voicemail to text. If one is developed, it will include a bunch of warnings regarding possible mistranslation, since an innocent comment might be mistranslated into threatening or insulting text, or urgent information might be miscommunicated and result in an inappropriate or delayed response, which could be costly.
Voicemail delivery via email is typically offered as a convenience to move file storage from a voicemail system. In a corporate environment, you might reduce these attachments by including your email address in your voicemail answering message, and/or by notifying correspondents that you prefer text to voice.