For this instructable to work it is important that you order tri-fold wedding announcement. It doesn't necessarily need to have the same orientation as mine, but this would be much more difficult with a bi-fold card.
-Tri-fold Wedding Announcement
-Musical Greeting Card
-Double Stick Tape
(1) Start by carefully cutting apart the two glued pages on your musical greeting card to expose the sound device and speaker.
(2) After cutting apart the card carefully cut out the sound device and speaker together, making sure to cut around the tab that extends to the other side of the card.
(3) Put a piece of clear packing tape on top of the small sound activation tab. Use a decent sized piece this is the key to making the sound work.
(4) Next, flip the card over and put strips of double stick tape on the back of the sound device and speaker.
(5) Position the sound assembly in the fold on back of your wedding announcement securing only the double stick tape. fold the card up and press to locate and secure the sound activation tab.
(6) Open the card and you should hear sweet music. If not check the positioning of the tab, and press the packing tape some more to make sure it is well stuck.
(7) Send the announcement and excitedly await reply.
My wife and I made these 3 years ago when we were engaged and sent out about 20. One of the cool things about it was that we were able to customize the cards with different songs according to whom we sent them to. All of the cards reached their destination and all worked.
P.S. The cards are perfectly fine to mail, but nothing beats the look on your friend's face when they open their hand delivered invitation, and it starts to play "Let's Get It On" by Marvin Gaye. (Yes, we did use that on one of them.)