Sorry if this is obvious -- it wasn't to me. I have Verizon service in the US - I don't know if this works generally. If you set the email address on an extension to a cellphone MMS (not SMS) address, and set it to deliver with the voice attachment, you'll get a playable voice message on your cellphone. The voice quality is excellent! So at least Verizon is able to convert the WAV file to a format for the MMS message. FYI the MMS address of a Verizon phone is email@example.com where nnnnnnnnnn is the phone's 10-digit number.