How can I send an MP3 via MMS or iMessage with my iPhone?
Even as of iOS 6, the iPhone offers no native ability to send an MP3 via MMS. Tapping and holding an MP3 file sent to your iPhone via email will offer a pop-up menu that will allow you to send the file via email, but not via MMS/iMessage.
There is a slightly tedious workaround, however.
1) From a desktop or laptop computer, send the MP3 to your phone as an MMS using the email to SMS method (read the old instructions at the bottom).2) Once you have received the MP3 as an MMS, you can then use the iPhone to forward it to others via MMS/iMessage.