Step 1: First, go to RadioShack and get all the parts you need
Here are the parts you'll need:
9V Recording Module - RadioShack catalogue number 276-1323 : $10.99
1/8" Mono Phone Plug - RadioShack catalogue number 274-0286 : $2.99 (pack of 2)
Enercell 9V Alkaline Battery - RadioShack catalogue number 230-0853 : $4.49
Also, you'll need a soldering gun and very thin solder.
Step 2: Solder The Phone Plug To The Mic Wires
Step 3: Finished product
Step 4: Next, go get the sound file
Mix your sound as you wish. Its easy to do: just drag and drop. The voice recorder can hold up to 20 seconds of sound.